“…We start by listing critical pairs of P 6 and P 10 . Observe that crit(P 6 ) = (0, 5), (1,6), (2,4), (3,9), (4, 7), (5, 7), (6,8) crit(P 10 ) = (0, 5), (1, 4), (2, 3), (3,9), (5, 7), (6,8) Observe also that any upper cover of P 6 has no irreducible elements. Therefore it must be one of the ordered sets listed in Fig.…”