two random processes on the time interval [0, 1] appear, roughly speaking, when conditioning the wiener process to vanish on both ends of [0,1]. with no further conditioning, the process takes both positive and negative values on [0, 1] and is called brownian bridge. conditioned also to stay positive on (0, 1), the process is called brownian excursion. in both cases a rigorous treatment involves a limiting procedure, since the formula "p"("a"|"b") = "p"("a" ∩ "b")/"p"("b") does not apply when "p"("b") = 0.