A method includes generating a model of a software program in which, at each cycle of the model, a program counter and at most one non-program-counter variable change value. The method also includes generating at least one disjunctive partition and/or at least one partial disjunctive partition for each variable of the model. The method also includes computing an image and/or a pre-image using partial disjunctive partitions. A model checker includes a modeler to generate a model of a software program in which, at each cycle of the model, a program counter and at most one non-program-counter variable change value.