(VAR y x)
(THEORY (C gcd))
(RULES
  le(0, y) -> true
  le(s(x), 0) -> false
  le(s(x), s(y)) -> le(x, y)
  minus(0, y) -> 0
  minus(s(x), y) -> if_minus(le(s(x), y), s(x), y)
  if_minus(true, s(x), y) -> 0
  if_minus(false, s(x), y) -> s(minus(x, y))
  gcd(0, y) -> y
  gcd(s(x), 0) -> s(x)
  gcd(s(x), s(y)) -> if_gcd(le(y, x), s(x), s(y))
  if_gcd(true, s(x), s(y)) -> gcd(minus(x, y), s(y))
  if_gcd(false, s(x), s(y)) -> gcd(minus(y, x), s(x))
)