(VAR x y) (RULES cond1(true,x,y) -> cond2(gr(x,0),x,y) cond2(true,x,y) -> cond1(gr(add(x,y),0),p(x),y) cond2(false,x,y) -> cond3(gr(y,0),x,y) cond3(true,x,y) -> cond1(gr(add(x,y),0),x,p(y)) cond3(false,x,y) -> cond1(gr(add(x,y),0),x,y) gr(0,x) -> false gr(s(x),0) -> true gr(s(x),s(y)) -> gr(x,y) add(0,x) -> x add(s(x),y) -> s(add(x,y)) p(0) -> 0 p(s(x)) -> x ) (COMMENT while gr(add(x,y),0) do if gr(x,0) then x:=p(x) else if gr(y,0) then y:=p(y) else skip fi fi od )