W Reconstructed

An early version of the Z Standard included the deductive systemW for reasoning about Z specifications. Later versions contain a different deductive system. In this paper we sketch a proof that W is relatively sound with respect to this new deductive system. We do this by demonstrating a semantic basis for a correspondence between the two systems, then showing that each of the inference rules ofW can be simulated as derived rules in the new system. These new rules are presented as tactics over the the inference rules of the new deductive system.