:- module accumbug.

:- interface.
:- import_module int.
:- func fact(int) = int.

:- implementation.

:- promise all [A, B, C, ABC] (A * B) * C = ABC: int <=> A * (B * C) = ABC.
%:- promise all [A, B, C, ABC] (A * B) * C = ABC <=> A * (B * C) = ABC.

fact(N) = (if N > 0 then N * fact(N - 1) else 1).