The type of elements.

A total ordering function to compare elements.

This is a two-argument function f such that f e1 e2 is zero if the elements 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.

The generic structural comparison function Stdlib.compare is a suitable ordering function for element types such as int or string.