Extended symbolic transition graphs with assignment

An extension of symbolic transition graphs with assignment is proposed which combines the advantages of both the assignment-before-action and the assignment-after-action approaches: like the former it allows a simple set of rules to be designed for generating finite symbolic graphs from regular value-passing process descriptions; like the later it avoids creating multiple copies in the graph for a recursive process definition. Experiences show that, in most cases, considerable reductions in verification time and space can be achieved using the new approach.