maximum(X,Y,X):-
	X>=Y.
maximum(X,Y,Y):-
	X<Y.

min(X,Y,X):-
	X=<Y,
	!.
min(_,Y,Y).

abs2(X,X) :- X >= 0, !.
abs2(X,Y) :- Y is -X.

fib(0,X):-X is 0.
fib(1,X):-X is 1.
fib(X,Y):-
	X>=2,
	X_Prime is X-1,
	X_PrimeTwo is X-2,
	fib(X_Prime,Y_Prime),
	fib(X_PrimeTwo,Y_PrimeTwo),
	Y is Y_Prime+Y_PrimeTwo.

divisor(X,Y,Z):-