fun gcd (a, 0) = a
      | (0, b) = b
      | (a, b) where (a < b)
               = gcd (a, b rem a)
      | (a, b) = gcd (b, a rem b)

fun lcm (a, b) = let val d = gcd (a, b)
                 in a * b div d
                 end