`type t = t`
`val compare : t -> t -> int`

A total ordering function This is a two-argument function `f` such that `f e1 e2` is zero if the values `e1` and `e2` are equal, `f e1 e2` is strictly negative if `e1` is smaller than `e2`, and `f e1 e2` is strictly positive if `e1` is greater than `e2`. Example: a suitable ordering function is the generic structural comparison function `Pervasives.compare`.