Generating Simpler CNF Formulae for SAT-Based LTL Model Checking

Since its introduction, Bounded Model Checking has been a motivating factor for the development of SAT solvers and considerable research has been directed towards them. However, while great advances have been made, other factors determining the overall runtime of the model-checking process have been afforded less attention. The process by which the CNF representation is obtained has a major effect on the time required to find a solution, as does the difficulty of the original propositional formula before this conversion. It has long been considered that the difficulty of a formula is directly related to its size, but it is only in recent times that ways of reducing this metric have been investigated within the framework of bounded model checking. This paper presents a comparison of some of this research, with the aim of highlighting its long overlooked importance, while noting that smaller formulae do not always require less time to solve.