type num
val (<) : num -> num -> bool
val (<=) : num -> num -> bool
val (>) : num -> num -> bool
val (>=) : num -> num -> bool
val (+) : num -> num -> num
val (-) : num -> num -> num
val ( * ) : num -> num -> num
val (/) : num -> num -> num
val (mod) : num -> num -> num
val string_of_num : num -> string
