Given a list of variables, and a list of literals that contain those variables, return a set. Each element of the set is an instantiation of the variables such that all instantiated literals are facts of the db. neg is an optional list of literals that must be false for an instantiation to be an answer. This is lazy, and will only be evaluated upon calls to iter, to_list or other similar functions. The answers will be cached in the set and readily available thereafter.
val cardinal : set -> intNumber of elements of the set
val pp_plan : Stdlib.Format.formatter -> set -> unitPrint query plan