Automatic Generation of Invariants in Spin

Spin takes a model to be veri ed and a property, and outputs true if the model satis es the property or otherwise false, with a counterexample. In the rst case, the user has no indication about why the property is satis ed. It may be the case that the model does not really represent what the user meant to express, and the property is void. It can therefore be useful if the tool could provide some additional information about the behavior of a model, regardless of a property's validity. A way of providing such information is to have Spin discover invariants of the model automatically. In this paper we focus on generating invariants of the form a rel b, where a and b are integer variables, and rel is an ordering relation. We give an algorithm with a matching implementation in Spin, including a graphical user interface.