| The comparison contract states that `sgn(compare(x, y)) == -sgn(compare(y, x))`. |
| (An immediate corollary is that `compare(x, x) == 0`.) This comparison |
| implementation either a) cannot return 0, b) cannot return a negative value but |
| may return a positive value, or c) cannot return a positive value but may return |
| a negative value. |
| |
| The results of violating this contract can include `TreeSet.contains` never |
| returning true or `Collections.sort` failing with an IllegalArgumentException |
| arbitrarily. |
| |
| In the long term, essentially all Comparators should be rewritten to use the |
| Java 8 Comparator factory methods, but our automated migration tools will, of |
| course, only work for correctly implemented Comparators. |
