Abstract: In a finite state machine (FSMverify) a set of goal states, to be searched for their reachability from a start state, is defined. An overapproximated path is found from a start state to a goal state by a forward approximation technique. The overapproximated path representation relies upon a partitioning of the state and input bits of FSMverify. A state matrix of the overapproximated path is organized by time-steps of FSMverify along a first dimension and by partitions of FSMverify state bits along a second dimension. An underapproximated path, along the path of the stepping stone matrix, is determined. Underapproximation is typically accomplished by simulation. A sequence of states to be output is updated with the underapproximated path. If a start to goal state sequence has been found, the procedure ends. Otherwise, the above steps of over and under approximation are repeated, using the results of the last underapproximation as a start state.