A B a b c d N S A B a b c d Φ max → e c = 0 → i = 0 a b c d N M A B a b c d A- B+ a b c d A- B+ a bc d e c t i t A- B+ a b c d e c t i t A B d c b a e c t i t A- B+ d c b a e c t i t A- B+ d c b a e c t i t