Reversing steps in membrane systems computations

The issue of reversibility in computational paradigms has gained interest in recent years. In this paper we investigate how to reverse steps in membrane systems computations. The problem is that computation steps in membrane systems do not preserve all the information that has to be used when reversing them. We try to formalize the relevant information needed, and we show that the proposed approach enjoy the so called loop lemma, which basically assures that the undoing obtained by reversely applying rules is correct.