4 combinations of ("B or C", "C or B") x ("X or Y", "Y or X").
By sorting, the conflict is given its canonical name, namely, "an
-early part became B or C, a late part becames X or Y", and whenever
+early part became B or C, a late part became X or Y", and whenever
any of these four patterns appear, and we can get to the same conflict
and resolution that we saw earlier.