(** This tactic solves the goal by contradiction, if in the hypothesis there are two terms `a<c` and `c<=a` *)
Ltac Order_mismatch :=
Clear_eq_;
match goal with
| id1:(?X1 < ?X2)%Z,id2:(?X2 <= ?X1)%Z |- _ =>
match goal with
| id1:(?X1 < ?X2)%Z,id2:(?X2 <= ?X1)%Z |- _ =>
first [ apply False_ind | apply False_rec ]; apply (Z.lt_irrefl X1);
apply Z.lt_le_trans with X2; assumption
end
| id2:(?X1 <= ?X2)%Z,id1:(?X2 < ?X1)%Z |- _ =>
match goal with
| id1:(?X1 < ?X2)%Z,id2:(?X2 <= ?X1)%Z |- _ =>
first [ apply False_ind | apply False_rec ]; apply (Z.lt_irrefl X1);
apply Z.lt_le_trans with X2; assumption
end
end.

Lemma h_sign_equal :
forall (a b c d : Z) (p : Qpositive)
(H_Qhomographic_sg_denom_nonzero1
H_Qhomographic_sg_denom_nonzero2 : Qhomographic_sg_denom_nonzero c d p),
h_sign a b c d p H_Qhomographic_sg_denom_nonzero1 =
h_sign a b c d p H_Qhomographic_sg_denom_nonzero2.