  In Zanardo, 1998, the Peircean semantics for branching-time logics is
enriched with a notion of indistinguishability at a moment t between histories
passing through t. Trees with indistinguishability relations provide a
semantics for a temporal language with tense and modal operators. In this paper
a notion of p-morphism and a notion of bisimulation, wrt this language and
semantics, are given and a number of preservation results are proven.
