The Free On-line Dictionary of Computing (30 December 2018):

B-Method

    A system for rigorous or formal
   development of software using the notion of Abstract
   Machines to specify and design software systems.  The
   B-Method is supported by the B-Toolkit.

   Abstract Machines are specified using the Abstract Machine
   Notation (AMN) which is in turn based on the mathematical
   theory of Generalised Substitutions.

   (1995-03-13)