  We present the implementation of pyB, a predicate - and expression - checker
for the B language. The tool is to be used for a secondary tool chain for data
validation and data generation, with ProB being used in the primary tool chain.
Indeed, pyB is an independent cleanroom-implementation which is used to
double-check solutions generated by ProB, an animator and model-checker for B
specifications. One of the major goals is to use ProB together with pyB to
generate reliable outputs for high-integrity safety critical applications.
Although pyB is still work in progress, the ProB/pyB toolchain has already been
successfully tested on various industrial B machines and data validation tasks.
