    """The general contract for values whose magnitude can be
       compared. `Comparable` imposes a total ordering upon
       instances of any type that satisfies the interface.

       If a type `T` satisfies `Comparable<T>`, then instances
       of `T` may be compared using the comparison operators
       `<`, `>`, `<=`, `>=`.

           assert (x>=0.0);

       A _ternary comparison_ is useful for asserting lower and
       upper bounds.

           assert (0.0<=x<1.0);

       Finally, the _compare_ operator `<=>` may be used to
       produce an instance of [[Comparison]].

           switch (x<=>y)
           case (equal) {
               print("same same");
           }
           case (smaller) {
               print("x smaller");
           }
           case (larger) {
               print("y smaller");
           }

       The total order of a type must be consistent with the
       definition of equality for the type. That is, there are
       three mutually exclusive possibilities:

       - `x<y`,
       - `x>y`, or
       - `x==y`

       (These possibilities are expressed by the enumerated
       instances [[smaller]], [[larger]], and [[equal]] of
       `Comparison`.)

       The order imposed by `Comparable` is sometimes called the
       _natural order_ of a type, to reflect the fact that any
       function of type `Comparison(T,T)` might determine a
       different order. Thus, some order-related operations come
       in two flavors: a flavor that depends upon the natural
       order, and a flavor which accepts an arbitrary comparator
       function. Examples are:

       - [[sort]] vs [[Iterable.sort]] and
       - [[max]] vs [[Iterable.max]]."""
    see (`class Comparison`)
    by ("Gavin")
    shared interface Comparable<in Other> of Other
            given Other satisfies Comparable<Other> {

        "Compares this value with the given value.
         Implementations must respect the constraints that:

         - `x==y` if and only if `x<=>y == equal`
            (consistency with `equals()`),
         - if `x>y` then `y<x` (symmetry), and
         - if `x>y` and `y>z` then `x>z` (transitivity)."
        see (`function equals`)
        shared formal Comparison compare(Other other);

        "Determines if this value is strictly larger than the
         given value."
        shared default Boolean largerThan(Other other)
                => compare(other)===larger;

        "Determines if this value is strictly smaller than the
         given value."
        shared default Boolean smallerThan(Other other)
                => compare(other)===smaller;

        "Determines if this value is larger than or equal to the
         given value."
        shared default Boolean notSmallerThan(Other other)
                => !compare(other)===smaller;

        "Determines if this value is smaller than or equal to
         the given value."
        shared default Boolean notLargerThan(Other other)
                => !compare(other)===larger;

    }