LOCAL Intensional.

Sum(s,y) <-
	 x In s &
	 Sum1(s\{x},x,y).

Sum1({}, x, x).
Sum1(s,x,x+w) <-
	      z In s &
	      Sum1(s\{z},z,w).

Max(s,y) <-
	 x In s &
	 Max1(s\{x},x,y).

Max1({},x,x).
Max1(s,x,y) <-
	    z In s &
	    IF z > x THEN Max1(s\{z},z,y) ELSE Max1(s\{z},x,y).

TwiceFloat(x, y) <- y = 2.0 * x.