Embodiments described herein relate to determining an abstraction of a computer program and to the refinement of an abstraction of a computer program. The computer program may be a sequential program or may be a concurrent (parallel) program. A directed graph represents a computer program and may be the cross product of threads within a concurrent program. Nodes within a representation of a program are reduced to a single node to produce an abstraction. An abstraction may be refined by determining constraints that produce a refined abstraction that does not comprise infeasible paths.