(VAR x y)
(RULES
lt(0,s(x)) -> true
lt(x,0) -> false
lt(s(x),s(y)) -> lt(x,y)
minus(x,y) -> help(lt(y,x),x,y)
help(true,x,y) -> s(minus(x,s(y)))
help(false,x,y) -> 0
)