  Petri net unfoldings are a useful tool to tackle state-space explosion in
verification and related tasks. Moreover, their structure allows to access
directly the relations of causal precedence, concurrency, and conflict between
events. Here, we explore the data structure further, to determine the following
relation: event a is said to reveal event b iff the occurrence of a implies
that b inevitably occurs, too, be it before, after, or concurrently with a.
Knowledge of reveals facilitates in particular the analysis of partially
observable systems, in the context of diagnosis, testing or verification; it
can also be used to generate more concise representations of behaviours via
abstractions. The reveals relation was previously introduced in the context of
fault diagnosis, where it was shown that the reveals relation was decidable:
for a given pair a,b in the unfolding U of a safe Petri net N, a finite prefix
P of U is sufficient to decide whether or not a reveals b. In this paper, we
first considerably improve the bound on |P|. We then show that there exists an
efficient algorithm for computing the relation on a given prefix. We have
implemented the algorithm and report on experiments.
