Linking VDM and Z

The International Grand Challenge in Verified Software is benchmarking current verification technology by conducting a series of experiments, and one such experiment is to build a verified POSIX-compliant flash filestore. An objective of this experiment is to combine different formal methods, and this raises issues about the different logics used. One significant area of difference is in the treatment of undefined expressions, and we show how this difference can be overcome using a unifying theory. This then allows us to use a theorem proverfor Z to verify theorems about a data type specified and refined in VDM.