1% Evan Tick (from Lisp version by R. P. Gabriel) 2% 3% (almost) Takeuchi function (recursive arithmetic) 4 5tak(R) :- tak(18, 12, 6, R). 6 7tak(X, Y, Z, A) :- 8 { 9 X =< Y, 10 Z = A 11 }. 12 13tak(X, Y, Z, A) :- 14 { 15 X >= Y+1 16 }, 17 tak(X-1, Y, Z, A1), 18 tak(Y-1, Z, X, A2), 19 tak(Z-1, X, Y, A3), 20 tak(A1, A2, A3, A ). 21