1. A method for verifying a digital system design, comprising: performing a first abstraction of a digital system design to obtain an abstract model of the digital system design; performing one or more first steps of a multiple-step model checking process using the abstract model, the multiple-step model checking process operable to verify the digital system design; during the multiple-step model checking process, performing a second abstraction to refine the abstract model; and performing one or more second steps of the multiple-step model checking process using the refined abstract model.