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85 matches found
X: 08, 104-117, LNM 511 (1976)
MEYER, Paul-André; YOR, Marc
Sur la théorie de la prédiction, et le problème de décomposition des tribus ${\cal F}^{\circ}_{t+}$ (General theory of processes)
This paper contains another version of Knight's theory (preceding paper 1007) for cadlag process instead of measurable processes. These results then are applied to the pathology of germ fields: a natural measurability conjecture does not hold, and an example is given of a process $X_t$ such that its natural $\sigma$-field ${\cal F}_{1+}$ is not generated by ${\cal F}_{1}$ and the germ-field at $0$ of the process $(X_{1+s})$
Comment: On the pathology of germ fields, see H. von Weizsäcker, Ann. Inst. Henri Poincaré, 19, 1983
Keywords: Prediction theory, Germ fields
Nature: Original
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X: 22, 481-500, LNM 511 (1976)
YOR, Marc
Sur les intégrales stochastiques optionnelles et une suite remarquable de formules exponentielles (Martingale theory, Stochastic calculus)
This paper contains several useful results on optional stochastic integrals of local martingales and semimartingales, as well as the first occurence of the well-known formula ${\cal E}(X)\,{\cal E}(Y)={\cal E}(X+Y+[X,Y])$ where ${\cal E}$ denotes the usual exponential of semimartingales. Also, the s.d.e. $Z_t=1+\int_0^t Z_sdX_s$ is solved, where $X$ is a suitable semimartingale, and the integral is an optional one. The Lévy measure of a local martingale is studied, and used to rewrite the Ito formula in a form that involves optional integrals. Finally, a whole family of exponentials'' is introduced, interpolating between the standard one and an exponential involving the Lévy measure, which was used by Kunita-Watanabe in a Markovian set-up
Keywords: Optional stochastic integrals, Stochastic exponentials, Lévy systems
Nature: Original
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XI: 14, 257-297, LNM 581 (1977)
YOR, Marc
Sur les théories du filtrage et de la prédiction (General theory of processes, Markov processes)
To be completed
Comment: MR 57, 10801
Keywords: Filtering theory, Prediction theory
Nature: Original
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XI: 34, 493-501, LNM 581 (1977)
YOR, Marc
A propos d'un lemme de Ch. Yoeurp (General theory of processes, Martingale theory)
Yoeurp's lemma is the following: if $A$ is a previsible process of bounded variation, its square bracket $[A,L]$ with any local martingale $L$ is a local martingale. This useful result was not easily accessible, thus a complete proof is given, with several new applications---in particular, this characterizes previsible processes of bounded variation among semimartingales
Keywords: Yoeurp's lemma, Square bracket
Nature: Original
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XI: 35, 502-517, LNM 581 (1977)
YOR, Marc
Remarques sur la représentation des martingales comme intégrales stochastiques (Martingale theory)
The main result on the relation between the previsible representation property of a set of local martingales and the extremality of their joint law appeared in a celebrated paper of Jacod-Yor, Z. für W-theorie, 38, 1977. Several concrete applications are given here, in particular a complete proof of a folklore'' result on the representation of local martingales of a Lévy process, and a discussion of the commutation problem of 1123
Comment: This is an intermediate paper between the Jacod-Yor results and the definitive version of previsible representation, using the theorem of Douglas, for which see 1221
Keywords: Previsible representation, Extreme points, Independent increments, Lévy processes
Nature: Original
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XI: 36, 518-528, LNM 581 (1977)
YOR, Marc
Sur quelques approximations d'intégrales stochastiques (Martingale theory)
The investigation concerns the limit of several families of Riemann sums, converging to the Ito stochastic integral of a continuous process with respect to a continuous semimartingale, to the Stratonovich stochastic integral, or to the Stieltjes integral with respect to the bracket of two continuous semimartingales. The last section concerns the stochastic integral of a differential form
Comment: Stratonovich stochastic integrals of differential forms have been extensively studied in the context of stochastic differential geometry: see among others Ikeda-Manabe Publ. RIMS, Kyoto Univ. 15, 1979; Bismut, Mécanique Aléatoire, Springer LNM~866, 1981; Meyer 1505
Keywords: Stochastic integrals, Riemann sums, Stratonovich integrals
Nature: Original
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XII: 09, 61-69, LNM 649 (1978)
YOR, Marc
Grossissement d'une filtration et semi-martingales~: théorèmes généraux (General theory of processes)
Given a filtration $({\cal F}_t)$ and a positive random variable $L$, the so-called progressively enlarged filtration is the smallest one $({\cal G}_t)$ containing $({\cal F}_t)$, and for which $L$ is a stopping time. The enlargement problem consists in describing the semimartingales $X$ of ${\cal F}$ which remain semimartingales in ${\cal G}$, and in computing their semimartingale characteristics. In this paper, it is proved that $X_tI_{\{t< L\}}$ is a semimartingale in full generality, and that $X_tI_{\{t\ge L\}}$ is a semimartingale whenever $L$ is honest for $\cal F$, i.e., is the end of an $\cal F$-optional set
Comment: This result was independently discovered by Barlow, Zeit. für W-theorie, 44, 1978, which also has a huge intersection with 1211. Complements are given in 1210, and an explicit decomposition formula for semimartingales in 1211
Keywords: Enlargement of filtrations, Honest times
Nature: Original
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XII: 11, 78-97, LNM 649 (1978)
JEULIN, Thierry; YOR, Marc
Grossissement d'une filtration et semi-martingales~: Formules explicites (General theory of processes)
This contains very substantial improvements on 1209, namely, the explicit computation of the characteristics of the semimartingales involved
Comment: For additional results on enlargements, see the two Lecture Notes volumes 833 (T. Jeulin) and 1118. See also 1350
Keywords: Enlargement of filtrations, Honest times
Nature: Original
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XII: 12, 98-113, LNM 649 (1978)
DELLACHERIE, Claude; MEYER, Paul-André; YOR, Marc
Sur certaines propriétés des espaces de Banach $H^1$ et $BMO$ (Martingale theory, Functional analysis)
The general subject is the weak topology $\sigma(H^1,BMO)$ on the space $H^1$. Its relatively compact sets are characterized by a uniform integrability property of the maximal functions. A sequential completeness result (a Vitali-Hahn-Saks like theorem) is proved. Finally, a separate section is devoted to the denseness of $L^\infty$ in $BMO$, a subject which has greatly progressed since (the Garnett-Jones theorem, see 1519; see also 3021 and 3316)
Keywords: Hardy spaces, $BMO$
Nature: Original
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XII: 21, 265-309, LNM 649 (1978)
YOR, Marc; SAM LAZARO, José de
Sous-espaces denses dans $L^1$ ou $H^1$ et représentation des martingales (Martingale theory)
This paper was a considerable step in the study of the general martingale problem, i.e., of the set ${\cal P}$ of all laws on a filtered measurable space under which a given set ${\cal N}$ of (adapted, right continuous) processes are local martingales. The starting point is a theorem from measure theory due to R.G. Douglas (Michigan Math. J. 11, 1964), and the main technical difference with preceding papers is the systematic use of stochastic integration in $H^1$. The main result can be stated as follows: given a law $P\in{\cal P}$, the set ${\cal N}$ has the previsible representation property, i.e., ${\cal F}_0$ is trivial and stochastic integrals with respect to elements of ${\cal N}$ are dense in $H^1$, if and only if $P$ is an extreme point of ${\cal P}$. Many examples and applications are given
Comment: The second named author's contribution concerns only the appendix on homogeneous martingales
Keywords: Previsible representation, Douglas theorem, Extremal laws
Nature: Original
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XII: 35, 482-488, LNM 649 (1978)
YOR, Marc; MEYER, Paul-André
Sur l'extension d'un théorème de Doob à un noyau $\sigma$-fini, d'après G. Mokobodzki (Measure theory)
Given a kernel $K(x,dy)$ consisting of probability measures, all of them absolutely continuous with respect to a measure $\mu$, Doob proved long ago using martingale theory that $K(x,dy)=k(x,y)\,\mu(dy)$ with a jointly measurable density $k(x,y)$. What happens if the measures $K(x,dy)$ are $\sigma$-finite? The answer is that Doob's result remains valid if $K$, considered as a mapping $x\mapsto K(x,\,.\,)$ taking values in the set of all $\sigma$-finite measures absolutely continuous w.r.t. $\mu$ (i.e., of classes of a.s. finite measurable functions), is Borel with respect to the topology of convergence in probability
Comment: The subject is discussed further in 1527. Note a mistake near the bottom of page 486: the $\sigma$-field on $E$ should be associated with the weak topology of $L[\infty$, or with the topology of $L^0$
Nature: Original
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XIII: 06, 90-115, LNM 721 (1979)
AZÉMA, Jacques; YOR, Marc
Une solution simple au problème de Skorokhod (Brownian motion)
An explicit solution is given to Skorohod's problem: given a distribution $\mu$ with mean $0$ and finite second moment $\sigma^2$, find a (non randomized) stopping time $T$ of a Brownian motion $(X_t)$ such that $X_T$ has the distribution $\mu$ and $E[T]=\sigma^2$. It is shown that if $S_t$ is the one-sided supremum of $X$ at time $t$, $T=\inf\{t:S_t\ge\psi(X_t)\}$ solves the problem, where $\psi(x)$ is the barycenter of $\mu$ restricted to $[x,\infty[$. The paper has several interesting side results, like explicit families of Brownian martingales, and a proof of the Ray-Knight theorem on local times
Comment: The subject is further investigated in 1356 and 1441. See also 1515. A general survey on the Skorohod embedding problem is Ob\lój, Probab. Surv. 1, 2004
Keywords: Skorohod imbedding
Nature: Original
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XIII: 29, 332-359, LNM 721 (1979)
JEULIN, Thierry; YOR, Marc
Inégalité de Hardy, semimartingales, et faux-amis (Martingale theory, General theory of processes)
The main purpose of this paper is to warn against obvious'' statements which are in fact false. Let $({\cal G}_t)$ be an enlargement of $({\cal F}_t)$. Assume that ${\cal F}$ has the previsible representation property with respect to a martingale $X$ which is a ${\cal G}$-semimartingale. Then it does not follow that every ${\cal F}$-martingale $Y$ is a ${\cal G}$-semimartingale. Also, even if $Y$ is a ${\cal G}$-semimartingale, its ${\cal G}$-compensator may have bad absolute continuity properties. The counterexample to the first statement involves a detailed study of the initial enlargement of the filtration of Brownian motion $(B_t)_{t\le 1}$ by the random variable $B_1$, which transforms it into the Brownian bridge, a semimartingale. Then the stochastic integrals with respect to $B$ which are ${\cal G}$-semimartingales are completely described, and this is the place where the classical Hardy inequality appears
Keywords: Hardy's inequality, Previsible representation
Nature: Original
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XIII: 30, 360-370, LNM 721 (1979)
JEULIN, Thierry; YOR, Marc
Sur l'expression de la dualité entre $H^1$ et $BMO$ (Martingale theory)
The problem is to find pairs of martingales $X,Y$ belonging to $H^1$ and $BMO$ such that the duality functional can be expressed as $E[X_{\infty}Y_{\infty}]$
Comment: On the same topic see 1518
Keywords: $BMO$, $H^1$ space, Hardy spaces
Nature: Original
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XIII: 34, 400-406, LNM 721 (1979)
YOR, Marc
Quelques épilogues (General theory of processes, Martingale theory, Stochastic calculus)
This is an account of current folklore, i.e., small remarks which settle natural questions, possibly published elsewhere but difficult to locate. Among the quotable results, one may mention that if a sequence of martingales converges in $L^1$, one can stop them at arbitrary large stopping times so that the stopped processes converge in $H^1$
Keywords: Local time, Enlargement of filtrations, $H^1$ space, Hardy spaces, $BMO$
Nature: Original
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XIII: 35, 407-426, LNM 721 (1979)
YOR, Marc
En cherchant une définition naturelle des intégrales stochastiques optionnelles (Stochastic calculus)
While the stochastic integral of a previsible process is a very natural object, the optional (compensated) stochastic integral is somewhat puzzling: it concerns martingales only, and depends on the probability law. This paper sketches a pedagogical'' approach, using a version of Fefferman's inequality for thin processes to characterize those thin processes which are jump processes of local martingales. The results of 1121, 1129 are easily recovered. Then an attempt is made to extend the optional integral to semimartingales
Keywords: Optional stochastic integrals, Fefferman inequality
Nature: Original
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XIII: 36, 427-440, LNM 721 (1979)
YOR, Marc
Les filtrations de certaines martingales du mouvement brownien dans ${\bf R}^n$ (Brownian motion)
The problem is to study the filtration generated by real valued stochastic integrals $Y=\int_0^t(AX_s, dX_s)$, where $X$ is a $n$-dimensional Brownian motion, $A$ is a $n\times n$-matrix, and $(\,,\,)$ is the scalar product. If $A$ is the identity matrix we thus get (squares of) Bessel processes. If $A$ is symmetric, we can reduce it to diagonal form, and the filtration is generated by a Brownian motion, the dimension of which is the number of different non-zero eigenvalues of $A$. In particular, this dimension is $1$ if and only if the matrix is equivalent to $cI_r$, a diagonal with $r$ ones and $n-r$ zeros. This is also (even if the symmetry assumption is omitted) the only case where $Y$ has the previsible representation property
Comment: Additional results on the same subject appear in 1545 and in Malric Ann. Inst. H. Poincaré 26 (1990)
Keywords: Stochastic integrals
Nature: Original
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XIII: 39, 453-471, LNM 721 (1979)
YOR, Marc
Sur le balayage des semi-martingales continues (General theory of processes)
For the general notation, see 1338. This paper is independent from the preceding one 1338, and some overlap occurs. The balayage formula is extended to processes $Z$ which are not locally bounded, and the local time of the semimartingale $Y$ is computed. The class of continuous semimartingales $X$ with canonical decomposition $X=M+V$ such that $dV$ is carried by $H=\{X=0\}$ is introduced and studied. It turns out to be an important class, closely related to relative martingales'' (Azéma, Meyer and Yor 2623). A number of results are given, too technical to be stated here. Stopping previsible, optional and progressive processes at the last exit time $L$ from $H$ leads to three $\sigma$-fields, ${\cal F}_L^p$, ${\cal F}_L^o$, ${\cal F}_L^{\pi}$, and it was considered surprising that the last two could be different (see 1240). Here it is shown that if $X$ is a continuous uniformly integrable martingale with $X_0=0$, $E[X_{\infty}|{\cal F}_L^o]=0\neq E[X_{\infty}|{\cal F}_L^{\pi}]$
Comment: See 1357
Keywords: Local times, Balayage, Balayage formula
Nature: Original
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XIII: 41, 478-487, LNM 721 (1979)
MEYER, Paul-André; STRICKER, Christophe; YOR, Marc
Sur une formule de la théorie du balayage (General theory of processes)
For the notation, see the review of 1340. It is shown here that under the same hypotheses, the semimartingale $Z_{g_t}X_t$ is a sum of three terms: the stochastic integral $\int_0^t \zeta_s dX_s$, where $\zeta$ is the previsible projection of $Z$, an explicit sum of jumps involving $Z-\zeta$, and a mysterious continuous process with finite variation $(R_t)$ such that $dR_t$ is carried by $H$, equal to $0$ if $Z$ was optional
Comment: See 1351, 1357
Keywords: Balayage, Balayage formula
Nature: Original
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XIII: 55, 624-624, LNM 721 (1979)
YOR, Marc
Un exemple de J. Pitman (General theory of processes)
The balayage formula allows the construction of many martingales vanishing on the zeros of a given continuous martingale $X$, namely martingales of the form $Z_{g_t}X_t$ where $Z$ is previsible. Taking $X$ to be Brownian motion, an example is given of a martingale vanishing on its zeros which is not of the above form
Comment: The general problem of finding all martingales which vanish on the zeros of a given continuous martingale is discussed by Azéma and Yor in 2622
Keywords: Balayage, Balayage formula
Nature: Exposition
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XIII: 56, 625-633, LNM 721 (1979)
AZÉMA, Jacques; YOR, Marc
Le problème de Skorokhod~: compléments à l'exposé précédent (Brownian motion)
What the title calls the preceding talk'' is 1306. The method is extended to (centered) measures possessing a moment of order one instead of two, preserving the uniform integrability of the stopped martingale
Comment: A general survey on the Skorohod embedding problem is Ob\lój, Probab. Surv. 1, 2004
Keywords: Skorohod imbedding
Nature: Original
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XIV: 06, 53-61, LNM 784 (1980)
AZÉMA, Jacques; GUNDY, Richard F.; YOR, Marc
Sur l'intégrabilité uniforme des martingales exponentielles (Martingale theory)
The main result of this paper is the following: Let $X$ be a martingale which is continuous and bounded in $L^1$ (both conditions are essential). Then $X$ is uniformly integrable if and only if $tP\{X^{*}>t\}$ or equivalently $tP\{S(X)>t\}$ tend to $0$ as $t\rightarrow\infty$, where $S(X)$ is the usual square function. The methods (using a good lambda inequality) are close to 1404
Comment: Generalized by Takaoka 3313
Keywords: Exponential martingales, Continuous martingales
Nature: Original
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XIV: 07, 62-75, LNM 784 (1980)
BARLOW, Martin T.; YOR, Marc
Sur la construction d'une martingale continue de valeur absolue donnée (Martingale theory)
This paper consists of two notes on Gilat's theorem (Ann. Prob. 5, 1977, See also 1358). The problem consists in constructing, given a continuous positive submartingale $Y$, a continuous martingale $X$ (possibly on a different space) such that $|X|$ has the same law as $Y$. Let $A$ be the increasing process associated with $Y$; it is necessary for the existence of $X$ that $dA$ should be carried by $\{Y=0\}$. This is shown by the first note (Yor's) to be also sufficient---more precisely, in this case the solutions of Gilat's problem are all continuous. The second note (Barlow's) shows how to construct a Gilat martingale by putting a random $\pm$ sign in front of each excursion of $Y$'', a simple intuitive idea and a delicate proof
Keywords: Gilat's theorem
Nature: Original
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XIV: 21, 189-199, LNM 784 (1980)
YOR, Marc
Application d'un lemme de Jeulin au grossissement de la filtration brownienne (General theory of processes, Brownian motion)
The problem considered here is the smallest enlargement of the Brownian filtration for which the process $\int_t^\infty B_s\mu(ds)$ is adapted, $\mu$ being a probability measure with a finite first moment
Comment: Note the misprint ${\cal G}$-martingale instead of ${\cal G}$-semimartingale in the statement of condition (H')
Keywords: Enlargement of filtrations
Nature: Original
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XIV: 22, 200-204, LNM 784 (1980)
AUERHAN, J.; LÉPINGLE, Dominique; YOR, Marc
Construction d'une martingale réelle continue de filtration naturelle donnée (General theory of processes)
It is proved in 1123 that, under a mere separability assumption, any filtration is the natural filtration of some bounded left-continuous increasing process $(A_t)$. If the filtration contains a Brownian motion $(B_t)$, then it is also the natural filtration of the continuous martingale $\int_0^t A_sdB_s$. Therefore, the natural filtration of (finitely or countably) many independent Brownian motions is generated by a single continuous martingale. Explicit constructions are discussed
Nature: Original
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XIV: 38, 343-346, LNM 784 (1980)
YOR, Marc
Remarques sur une formule de Paul Lévy (Brownian motion)
Given a two-dimensional Brownian motion $(X_t,Y_t)$, Lévy's area integral formula gives the characteristic function $E[\,\exp(iu\int_0^1 X_s\,dY_s-Y_s\,dX_s)\,\,|\,\, X_0=x, Y_0=y]$. A short proof of this formula is given, and it is shown how to deduce from it the apparently more general $E[\exp(iu\int_0^1 X_sdY_s+iv\int_0^1 Y_sdX_s)\,]$ computed by Berthuet
Keywords: Area integral formula
Nature: Original
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XIV: 48, 496-499, LNM 784 (1980)
COCOZZA-THIVENT, Christiane; YOR, Marc
Démonstration d'un théorème de F. Knight à l'aide de martingales exponentielles (Martingale theory)
This is a new proof of Knight's theorem that (roughly) finitely many orthogonal continuous local martingales, when separately time-changed into Brownian motions, become independent. A similar theorem for the Poisson case is proved in the same way
Comment: See 518 for an earlier proof
Keywords: Changes of time
Nature: Original
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XV: 15, 210-226, LNM 850 (1981)
JEULIN, Thierry; YOR, Marc
Sur les distributions de certaines fonctionnelles du mouvement brownien (Brownian motion)
This paper gives new proofs and extensions of results due to Knight, concerning occupation times by the process $(S_t,B_t)$ up to time $T_a$, where $(B_t)$ is Brownian motion, $T_a$ the hitting time of $a$, and $(S_t)$ is $\sup_{s\le t} B_s$. The method uses enlargement of filtrations, and martingales similar to those of 1306. Theorem 3.7 is a decomposition of Brownian paths akin to Williams' decomposition
Keywords: Explicit laws, Occupation times, Enlargement of filtrations, Williams decomposition
Nature: Original
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XV: 35, 526-528, LNM 850 (1981)
YOR, Marc
Sur certains commutateurs d'une filtration (General theory of processes)
Let $({\cal F}_t)$ be a filtration satisfying the usual conditions and ${\cal G}$ be a $\sigma$-field. Then the conditional expectation $E[.|{\cal G}]$ commutes with $E[.|{\cal F}_T]$ for all stopping times $T$ if and only if for some stopping time $S$ ${\cal G}$ lies between ${\cal F}_{S-}]$ and ${\cal F}_S]$
Keywords: Conditional expectations
Nature: Original
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XV: 40, 590-603, LNM 850 (1981)
STROOCK, Daniel W.; YOR, Marc
Some remarkable martingales (Martingale theory)
This is a sequel to a well-known paper by the authors (Ann. ENS, 13, 1980) on the subject of pure martingales. A continuous martingale $(M_t)$ with $<M,M>_{\infty}=\infty$ is pure if the time change which reduces it to a Brownian motion $(B_t)$ entails no loss of information, i.e., if $M$ is measurable w.r.t. the $\sigma$-field generated by $B$. The first part shows the purity of certain stochastic integrals. Among the striking examples considered, the stochastic integrals $\int_0^t B^n_sdB_s$ are extremal for every integer $n$, pure for $n$ odd, but nothing is known for $n$ even. A beautiful result unrelated to purity is the following: complex Brownian motion $Z_t$ starting at $z_0$ and its (Lévy) area integral generate the same filtration if and only if $z_0\neq0$
Keywords: Pure martingales, Previsible representation
Nature: Original
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XV: 41, 604-617, LNM 850 (1981)
LÉPINGLE, Dominique; MEYER, Paul-André; YOR, Marc
Extrémalité et remplissage de tribus pour certaines martingales purement discontinues (General theory of processes, Martingale theory)
This paper consists roughly of two parts. First, the study of a filtration where all martingales are purely discontinuous, and jump on a given well-ordered optional set. Then under a simple separability assumption, one can construct one single martingale which generates the filtration. The second part deals with the same problem as in 1540, but replacing continuous martingales by purely discontinuous martingales with unit jumps, and Brownian motion by a Poisson process. It is shown that the situation is much simpler, purity and extremality being equivalent in this case
Keywords: Poisson processes, Pure martingales, Previsible representation, Jumps
Nature: Original
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XVI: 17, 213-218, LNM 920 (1982)
FALKNER, Neil; STRICKER, Christophe; YOR, Marc
Temps d'arrêt riches et applications (General theory of processes)
This paper starts from the existence of increasing left-continuous processes $(A_t)$ which generate the previsible $\sigma$-field, i.e., every previsible process can be represented as $f(X_t)$ for some Borel function $f$ (see 1123), to prove the existence (discovered by the first named author) of rich'' stopping times $T$, i.e., previsible stopping times which encode the whole past up to time $T$: $\sigma(T)={\cal F}_{T-}$ (a few details are omitted here). This result leads to counterexamples: a non-reversible semimartingale (see the preceding paper 1616) and a stopping time $T$ for Brownian motion such that $L^a_T$ is not a semimartingale in its space variable $a$
Keywords: Stopping times, Local times, Semimartingales, Previsible processes
Nature: Original
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XVI: 19, 221-233, LNM 920 (1982)
YOR, Marc
Application de la relation de domination à certains renforcements des inégalités de martingales (Martingale theory)
The domination relation (Lenglart 1977) between a positive, right-continuous process $X$ and a previsible increasing process $A$ holds whenever $E[X_T]\le E[A_T]$ at stopping times. It plays an important role in the paper 1404 of Lenglart-Lepingle-Pratelli on martingale inequalities. Here it is shown to imply a general inequality involving $X^\ast_{\infty}$ and $1/A_{\infty}$, from which follow a number of inequalities for a continuous local martingale $M$. Among them, estimates on the ratios of the three quantities $M^\ast_{\infty}$, $<M>_{\infty}$, $\sup_{a,t} L^a_t$. One can recover also the stronger version of Doob's inequality, proved by Pitman 1517
Comment: See an earlier paper of the author on this subject, Stochastics, 3, 1979. The author mentions that part of the results were discovered slightly earlier by R.~Gundy
Keywords: Martingale inequalities, Domination inequalities
Nature: Original
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XVI: 21, 238-247, LNM 920 (1982)
YOR, Marc
Sur la transformée de Hilbert des temps locaux browniens et une extension de la formule d'Itô (Brownian motion)
This paper is about the application to the function $(x-a)\log|x-a|-(x-a)$ (whose second derivative is $1/x-a$) of the Ito-Tanaka formula; the last term then involves a formal Hilbert transform $\tilde L^a_t$ of the local time process $L^a_t$. Such processes had been defined by Ito and McKean, and studied by Yamada as examples of Fukushima's additive functionals of zero energy''. Here it is proved, as a consequence of a general theorem, that this process has a jointly continuous version---more precisely, Hölder continuous of all orders $<1/2$ in $a$ and in $t$
Comment: For a modern version with references see Yor, Some Aspects of Brownian Motion II, Birkhäuser 1997
Keywords: Local times, Hilbert transform, Ito formula
Nature: Original
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XVII: 08, 81-88, LNM 986 (1983)
LE GALL, Jean-François; YOR, Marc
Sur l'équation stochastique de Tsirelson
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XVII: 09, 89-105, LNM 986 (1983)
YOR, Marc
Le drap brownien comme limite en loi des temps locaux linéaires (Brownian motion, Local time, Brownian sheet)
A central limit theorem is obtained for the increments $L^x_t-L^0_t$ of Brownian local times. The limiting process is expressed in terms of a Brownian sheet, independent of the initial Brownian motion
Comment: This type of result is colsely related to the Ray-Knight theorems, which describe the law of Brownian local times considered at certain random times. This has been extended first by Rosen in 2533, where Brownian motion is replaced with a symmetric stable process, then by Eisenbaum 2926
Keywords: Brownian motion, Several parameter processes
Nature: Original
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XIX: 29, 332-349, LNM 1123 (1985)
YOR, Marc
Compléments aux formules de Tanaka-Rosen (Brownian motion)
Several variants of Rosen's works (Comm. Math. Phys. 88 (1983), Ann. Proba. 13 (1985), Ann. Proba. 14 (1986)) are presented. They yield Tanaka-type formulae for the self-intersection local times of Brownian motion in dimension 2 and beyond, establishing again Varadhan's normalization result (Appendix to Euclidean quantum field theory, by K.~Symanzik, in Local Quantum Theory, Academic Press, 1969). The methods involve stochastic calculus, which was not needed in 1928
Comment: Examples of further work on this subject, using stochastic calculus or not, are Werner, Ann. I.H.P. 29 (1993) who gives many references, Khoshnevisan-Bass, Ann. I.H.P. 29 (1993), Rosen-Yor Ann. Proba. 19 (1991)
Keywords: Brownian motion, Local times, Self-intersection
Nature: Original proofs
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XIX: 30, 350-365, LNM 1123 (1985)
YOR, Marc
Renormalisation et convergence en loi pour des temps locaux d'intersection du mouvement brownien dans ${\bf R}^3$ (Brownian motion)
It is shown that no renormalization à la Varadhan occurs for the self-intersection local times of 3-dimensional Brownian motion; but a weaker result is established: when the point $y\inR^3$ tends to $0$, the self-intersection local time at $y$, on the triangle $\{0<s<u\le t\},\ t\ge0$, centered and divided by $(-\log|y|)^{1/2}$, converges in law to a Brownian motion. Several variants of this theorem are established
Comment: This result was used by Le Gall in his work on fluctuations of the Wiener sausage: Ann. Prob. 16 (1988). Many results by Rosen have the same flavour
Keywords: Brownian motion, Local times, Self-intersection
Nature: Original
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XX: 34, 532-542, LNM 1204 (1986)
YOR, Marc
Précisions sur l'existence et la continuité des temps locaux d'intersection du mouvement brownien dans ${\bf R}^2$
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XX: 35, 543-552, LNM 1204 (1986)
YOR, Marc
Sur la représentation comme intégrales stochastiques des temps d'occupation du mouvement brownien dans ${\bf R}^d$ (Brownian motion)
Varadhan's renormalization result (Appendix to Euclidean quantum field theory, by K.~Symanzik, in Local Quantum Theory consists in centering certain sequences of Brownian functionals and showing $L^2$-convergence. The same results are obtained here by writing these centered functionals as stochastic integrals
Comment: One of mny applications of stochastic calculus to the existence and regularity of self-intersection local times. See Rosen's papers on this topic in general, and page 196 of Le Gall, École d'Été de Saint-Flour XX, Springer LNM 1527
Keywords: Local times, Self-intersection, Previsible representation
Nature: Original proofs
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XXI: 15, 230-245, LNM 1247 (1987)
SONG, Shiqi; YOR, Marc
Inégalités pour les processus self-similaires arrêtés à un temps quelconque
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XXI: 17, 262-269, LNM 1247 (1987)
AZÉMA, Jacques; YOR, Marc
Interprétation d'un calcul de H. Tanaka en théorie générale des processus
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XXI: 18, 270-275, LNM 1247 (1987)
BIANE, Philippe; LE GALL, Jean-François; YOR, Marc
Un processus qui ressemble au pont brownien
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XXI: 23, 375-403, LNM 1247 (1987)
CALAIS, J.-Y.; YOR, Marc
Renormalisation et convergence en loi pour certaines intégrales multiples associées au mouvement brownien dans ${\bf R}^d$
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XXII: 23, 217-224, LNM 1321 (1988)
YOR, Marc
Remarques sur certaines constructions des mouvements browniens fractionnaires
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XXII: 24, 225-248, LNM 1321 (1988)
WEINRYB, Sophie; YOR, Marc
Le mouvement brownien de Lévy indexé par ${\bf R}^3$ comme limite centrale de temps locaux d'intersection
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XXII: 34, 454-466, LNM 1321 (1988)
BIANE, Philippe; YOR, Marc
Sur la loi des temps locaux browniens pris en un temps exponentiel
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XXIII: 07, 88-130, LNM 1372 (1989)
AZÉMA, Jacques; YOR, Marc
Étude d'une martingale remarquable
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XXIII: 23, 275-293, LNM 1372 (1989)
BARLOW, Martin T.; PITMAN, James W.; YOR, Marc
On Walsh's Brownian motions
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XXIII: 24, 294-314, LNM 1372 (1989)
BARLOW, Martin T.; PITMAN, James W.; YOR, Marc
Une extension multidimensionnelle de la loi de l'arc sinus
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XXIII: 25, 315-323, LNM 1372 (1989)
DONATI-MARTIN, Catherine; YOR, Marc
Mouvement brownien et inégalité de Hardy dans $L^2$
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XXIV: 14, 210-226, LNM 1426 (1990)
AZÉMA, Jacques; YOR, Marc
Dérivation par rapport au processus de Bessel
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XXIV: 15, 227-265, LNM 1426 (1990)
JEULIN, Thierry; YOR, Marc
Filtration des ponts browniens et équations différentielles stochastiques linéaires
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XXV: 23, 284-290, LNM 1485 (1991)
DUBINS, Lester E.; ÉMERY, Michel; YOR, Marc
A continuous martingale in the plane that may spiral away to infinity
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XXVI: 22, 249-306, LNM 1526 (1992)
AZÉMA, Jacques; YOR, Marc
Sur les zéros des martingales continues
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XXVI: 23, 307-321, LNM 1526 (1992)
AZÉMA, Jacques; MEYER, Paul-André; YOR, Marc
Martingales relatives
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XXVI: 24, 322-347, LNM 1526 (1992)
JEULIN, Thierry; YOR, Marc
Une décomposition non-canonique du drap brownien (Brownian sheet, Gaussian processes)
In 2415, the authors have introduced a transform of Brownian motion. Here, a similar transform is defined on the Brownian sheet; this transform is shown to be strongly mixing
Comment: This work was motivated by Föllmer's article on Martin boundaries on Wiener space (in Diffusion processes and related problems in analysis, vol.~I, Birkhäuser 1990)
Keywords: Brownian motion, Several parameter processes
Nature: Original
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XXVII: 08, 53-77, LNM 1557 (1993)
JEULIN, Thierry; YOR, Marc
Moyennes mobiles et semimartingales
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XXVII: 14, 122-132, LNM 1557 (1993)
DUBINS, Lester E.; ÉMERY, Michel; YOR, Marc
On the Lévy transformation of Brownian motions and continuous martingales
An erratum is given in 4421 in Volume XLIV.
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XXVII: 15, 133-158, LNM 1557 (1993)
AZÉMA, Jacques; JEULIN, Thierry; KNIGHT, Frank B.; YOR, Marc
Le théorème d'arrêt en une fin d'ensemble prévisible
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XXVII: 16, 159-172, LNM 1557 (1993)
ELWORTHY, Kenneth David; YOR, Marc
Conditional expectations for derivatives of certain stochastic flows
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XXVII: 17, 173-176, LNM 1557 (1993)
WALSH, John B.; YOR, Marc
Some remarks on $A(t,B_t)$
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XXX: 16, 243-254, LNM 1626 (1996)
AZÉMA, Jacques; RAINER, Catherine; YOR, Marc
Une propriété des martingales pures
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XXX: 20, 312-343, LNM 1626 (1996)
AZÉMA, Jacques; JEULIN, Thierry; KNIGHT, Frank B.; MOKOBODZKI, Gabriel; YOR, Marc
Sur les processus croissants de type injectif
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XXXI: 12, 113-125, LNM 1655 (1997)
ELWORTHY, Kenneth David; LI, Xu-Mei; YOR, Marc
On the tails of the supremum and the quadratic variation of strictly local martingales (Martingale theory)
The asymptotic tails of the current maximum and the quadratic variation of a positive continuous local martingale are compared. Applications to strict local martingales associated with transient diffusions, such as Bessel processes, and remarkable identities for Bessel functions are given
Comment: In discrete time, see the following article 3113. Related results are due to Takaoka 3313
Keywords: Continuous martingales, Local martingales, Quadratic variation, Maximal process
Nature: Original
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XXXI: 27, 272-286, LNM 1655 (1997)
PITMAN, James W.; YOR, Marc
On the lengths of excursions of some Markov processes
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XXXI: 28, 287-305, LNM 1655 (1997)
PITMAN, James W.; YOR, Marc
On the relative lengths of excursions derived from a stable subordinator
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XXXI: 29, 306-314, LNM 1655 (1997)
YOR, Marc
Some remarks about the joint law of Brownian motion and its supremum (Brownian motion)
Seshadri's identity says that if $S_1$ denotes the maximum of a Brownian motion $B$ on the interval $[0,1]$, the r.v. $2S_1(S_1-B_1)$ is independent of $B_1$ and exponentially distributed. Several variants of this are obtained
Nature: Original
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XXXII: 17, 237-249, LNM 1686 (1998)
DONEY, R.A.; WARREN, Jonathan; YOR, Marc
Perturbed Bessel processes
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XXXII: 19, 264-305, LNM 1686 (1998)
BARLOW, Martin T.; ÉMERY, Michel; KNIGHT, Frank B.; SONG, Shiqi; YOR, Marc
Autour d'un théorème de Tsirelson sur des filtrations browniennes et non browniennes (Brownian motion, Filtrations)
Tsirelson has shown that no Walsh's Brownian motion with three rays or more can live in a Brownian filtration (GAFA 7, 1997). Using his methods, the result is extended to spider martingales. A conjecture of M. Barlow is also proved: if $L$ is an honest time in a (possibly multidimensional, Brownian filtration, then ${\cal F}_{L+}$ is generated by ${\cal F}_{L}$ and at most one event. Last, it is shown that a Walsh's Brownian motion can live in the filtration generated by another Walsh's Brownian motion only if the former is obtained from the latter by aggregating rays
Comment: On Tsirelson's theorem, see also Tsirelson, ICM 1998 vol. III, and M. Émery, Astérisque 282 (2002). A simplified proof of Barlow's conjecture is given in 3304. For more on Théorème 1 (Slutsky's lemma), see 3221 and 3325
Keywords: Filtrations, Spider martingales, Walsh's Brownian motion, Cosiness, Slutsky's lemma
Nature: New exposition of known results, Original additions
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XXXII: 20, 306-312, LNM 1686 (1998)
ÉMERY, Michel; YOR, Marc
Sur un théorème de Tsirelson relatif à des mouvements browniens corrélés et à la nullité de certains temps locaux
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XXXII: 22, 316-327, LNM 1686 (1998)
AZÉMA, Jacques; JEULIN, Thierry; KNIGHT, Frank B.; YOR, Marc
Quelques calculs de compensateurs impliquant l'injectivité de certains processus croissants
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XXXII: 23, 328-342, LNM 1686 (1998)
WARREN, Jonathan; YOR, Marc
The Brownian burglar: conditioning Brownian motion by its local time process
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XXXIV: 20, 417-431, LNM 1729 (2000)
VOSTRIKOVA, Lioudmilla; YOR, Marc
Some invariance properties (of the laws) of Ocone's martingales
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XXXV: 23, 334-347, LNM 1755 (2001)
CHAUMONT, Loïc; HOBSON, David G.; YOR, Marc
Some consequences of the cyclic exchangeability property for exponential functionals of Lévy processes
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XXXVIII: 05, 42-69, LNM 1857 (2005)
NGUYEN-NGOC, Laurent; YOR, Marc
Some martingales associated to reflected Lévy processes

XXXIX: 08, 157-170, LNM 1874 (2006)
Ito's integrated formula for strict local martingales

XXXIX: 15, 305-336, LNM 1874 (2006)
ROYNETTE, Bernard; VALLOIS, Pierre; YOR, Marc
Pénalisations et quelques extensions du théorème de Pitman, relatives au mouvement brownien et à son maximum unilatère

XXXIX: 16, 337-356, LNM 1874 (2006)
GALLARDO, Léonard; YOR, Marc
Some remarkable properties of the Dunkl martingales

XL: 14, 265-285, LNM 1899 (2007)
SALMINEN, Paavo; YOR, Marc
Tanaka formulae for symmetric Lévy processes

XLII: 08, 187-227, LNM 1978 (2009)
YANO, Kouji; YANO, Yuko; YOR, Marc
On the laws of first hitting times of points for one-dimensional symmetric stable Lévy processes (Theory of Lévy processes)
Nature: Original
XLIII: 19, 437-439, LNM 2006 (2011)
BAKER, David; YOR, Marc
On martingales with given marginals and the scaling property (Martingale theory, Theory of Brownian motion)
Nature: Original
XLIII: 20, 441-449, LNM 2006 (2011)
BAKER, David; DONATI-MARTIN, Catherine; YOR, Marc
A sequence of Albin type continuous martingales with Brownian marginals and scaling (Martingale theory)
Keywords: Martingales, Brownian marginals
Nature: Original
XLIII: 21, 451-503, LNM 2006 (2011)
HIRSCH, Francis; PROFETA, Christophe; ROYNETTE, Bernard; YOR, Marc
Constructing self-similar martingales via two Skorokhod embeddings (Martingale theory)
Keywords: Skorokhod embeddings, Hardy-Littlewood functions, Convex order, Schauder fixed point theorem, Self-similar martingales, Karamata's representation theorem
Nature: Original
XLIV: 21, 467-467, LNM 2046 (2012)
ÉMERY, Michel; YOR, Marc
Erratum to Séminaire XXVII
This is an erratum to 2714.
Keywords: Brownian motion, Continuous martingale
Nature: Erratum