Φ max → e c = 0 → i = 0 a b c d N M N S d c b a N- Φ ≠ 0 → e c ≠ 0 (dcba) → i ≠ 0 (MN) M+ Φ = 0 → e c max (dcba) → i max (MN) a bc d N- M+ d c b a N- Φ ≠ 0 → e c ≠ 0 (dcba) → i ≠ 0 (MN) M+ Φ max → e c = 0 → i = 0 a b c d N M a b c d M- Φ ≠ 0 → e c ≠ 0 (abcd) → i ≠ 0 (NM) N+ a b c d Φ = 0 → e c max (abcd)→ i max (NM) M- N+ a b c d M- Φ ≠ 0 → e c ≠ 0 (abcd) → i ≠ 0 (NM) N+ Φ max → e c = 0 → i = 0 a b c d N M