1. A method carried out on a computer of verifying properties of a system, the method comprising the steps of: applying to said system input signals that are subject to imposed constraints, using a verification tool, identifying states of said system that are non-returnable states, and when said step of using a verification tool determines that there exist non-returnable states in said system, outputting an alert signal that informs an operator that said imposed constraints are mutually inconsistent or that there is a design error in said system, and conversely, when said step of using said verification tool determines that said imposed constraints are mutually consistent and no error determinations are made in the course of said applying said input signals, outputting a signal to said operator that indicates consistency of said properties.