Absolute value of a number abs/2 - back to content


	
		?- abs(0,R).
		R = 0
		?- abs(-9,R).
		R = 9
		?- abs(-9,9).
		yes
		?- abs(-9,8).
		no
		?- abs(I,8).
		I = 8



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