Original article at: http://www.math.washington.edu/~ejpecp/viewarticle.php?id=1259

Martingales on Random Sets and the Strong Martingale Property

Michael J. Sharpe, University of California, San Diego

Abstract

Let X be a process defined on an optional random set. The paper develops two different conditions on X guaranteeing that it is the restriction of a uniformly integrable martingale. In each case, it is supposed that X is the restriction of some special semimartingale Z with canonical decomposition Z=M+A. The first condition, which is both necessary and sufficient, is an absolute continuity condition on A. Under additional hypotheses, the existence of a martingale extension can be characterized by a strong martingale property of X. Uniqueness of the extension is also considered.

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Original article at: http://www.math.washington.edu/~ejpecp/viewarticle.php?id=1259