Lemma sg_neg_2 : forall (a b c d : Z) (p : Qpositive) (H_Qhomographic_sg_denom_nonzero : Qhomographic_sg_denom_nonzero c d p) (na nb nc nd : Z) (np : Qpositive), Qhomographic_sign a b c d p H_Qhomographic_sg_denom_nonzero = ((-1)%Z, (na, (nb, (nc, nd)), np)) -> {(0 <= na)%Z /\ (0 <= nb)%Z /\ (nc <= 0)%Z /\ (nd <= 0)%Z} + {(na <= 0)%Z /\ (nb <= 0)%Z /\ (0 <= nc)%Z /\ (0 <= nd)%Z} + {np = One}.