| 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. |