Lemma
spec_Qquadratic_Qpositive_to_Q_spec_Qquadratic_Qpositive_to_Qpositive2_pos :
forall (a b c d e f g h : Z) (p1 p2 : Qpositive),
Qsgn (spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2) = 1%Z ->
spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2 =
Qpos (spec_Qquadratic_Qpositive_to_Qpositive2 a b c d e f g h p1 p2).
(** We use this when (Z.sgn a+b+c+d)<0 *)
Lemma
spec_Qquadratic_Qpositive_to_Q_spec_Qquadratic_Qpositive_to_Qpositive2_neg_1
:
forall (a b c d e f g h : Z) (p1 p2 : Qpositive),
Qsgn (spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2) = (-1)%Z ->
spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2 =
Qneg
(spec_Qquadratic_Qpositive_to_Qpositive2 (- a) (- b)
(- c) (- d) e f g h p1 p2).
(** We use this when 0<=(Z.sgn a+b+c+d) *)
Lemma
spec_Qquadratic_Qpositive_to_Q_spec_Qquadratic_Qpositive_to_Qpositive2_neg_2
:
forall (a b c d e f g h : Z) (p1 p2 : Qpositive),
Qsgn (spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2) = (-1)%Z ->
spec_Qquadratic_Qpositive_to_Q a b c d e f g h p1 p2 =
Qneg
(spec_Qquadratic_Qpositive_to_Qpositive2 a b c d
(- e) (- f) (- g) (- h) p1 p2).

Lemma a_field_equality_4 :
forall a b c d e f g h q1 q2 : Q,
g <> Zero ->
Qmult a g = Qmult c e ->
Qmult b g = Qmult c f ->
Qmult c h = Qmult d g ->
Qplus (Qplus (Qplus (Qmult (Qmult e q1) q2) (Qmult f q1)) (Qmult g q2)) h <>
Zero ->
Qmult c (Qinv g) =
Qmult
(Qplus (Qplus (Qplus (Qmult (Qmult a q1) q2) (Qmult b q1)) (Qmult c q2)) d)
(Qinv
(Qplus
(Qplus (Qplus (Qmult (Qmult e q1) q2) (Qmult f q1)) (Qmult g q2)) h)).