  Step net bisimilarity \cite{Gor23} is a truly concurrent behavioral
equivalence for finite Petri nets, which is defined as a smooth generalization
of standard step bisimilarity \cite{NT84} on Petri nets, but with the property
of relating markings (of the same size only) generating the same partial orders
of events. The process algebra FNM \cite{Gor17} truly represents all (and only)
the finite Petri nets, up to isomorphism. We prove that step net bisimilarity
is a congruence w.r.t. the FMN operators, In this way, we have defined a
compositional semantics, fully respecting causality and the branching structure
of systems, for the class of all the finite Petri nets.
