%Source: Random examples used for debugging termination analysis for arithmetic Prolog programs % terminating % Implements calculation of the Ackermann function. % Direct implementation of the recursive definition by Péter (1935) % First attempt did not check for X > 0, Y > 0 in last case. Was found nonterminating by aprove %query:ackermann(b,b,f). ackermann(X, Y, Z) :- X =:= 0, Y >= 0, !, Z is Y + 1. ackermann(X, Y, Z) :- X > 0, Y =:= 0, !, ackermann(X - 1, 1, Z). ackermann(X, Y, Z) :- X > 0, Y > 0, !, ackermann(X, Y - 1, W), ackermann(X - 1, W, Z).
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