A function that maps predicates to predicates. Specifically, the predicate transformer for some statement S is a function that maps some predicate R into the weakest precondition of S with respect to R. The term was introduced by Dijkstra in 1975 in conjunction with a calculus for the derivation of programs; this provides for development of a program to be guided by the simultaneous development of a total correctness proof for the program. See program correctness proof.