(VAR x y)
(RULES
cond(true,x,y) -> cond(gr(x,y),y,x)
gr(0,x) -> false
gr(s(x),0) -> true
gr(s(x),s(y)) -> gr(x,y)
)
(COMMENT
while gr(x,y)
do
	x,y:=y,x
od
)