Starting from a compositional operational semantics of transition P Systems
we have previously defined, we face the problem of developing an axiomatization that is
sound and complete with respect to some behavioural equivalence. To achieve this goal,
we propose to transform the systems into a unique normal form which preserves the
semantics. As a first step, we introduce axioms which allow the transformation of mem-
brane structures with no dissolving rules into flat membranes. We discuss the problems
which arise when dissolving rules are allowed and we suggest possible solutions. We leave
as future work the further step that leads to the wanted normal form
