(STRATEGY
    INNERMOST)

(VAR
    x y)
(DATATYPES
    A = µX.< 0, true, s(X), false >)
(SIGNATURES
    le :: [A x A] -> A
    minus :: [A x A] -> A
    gcd :: [A x A] -> A
    if_gcd :: [A x A x A] -> A)
(RULES
    le(0(),y) -> true()
    le(s(x),0()) -> false()
    le(s(x),s(y)) -> le(x,y)
    minus(x,0()) -> x
    minus(s(x),s(y)) -> 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)))