diff options
Diffstat (limited to 'theories/Init/Logic.v')
| -rw-r--r-- | theories/Init/Logic.v | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/theories/Init/Logic.v b/theories/Init/Logic.v index 85123cc44..9b58c524e 100644 --- a/theories/Init/Logic.v +++ b/theories/Init/Logic.v @@ -125,6 +125,25 @@ Proof. [apply Hl | apply Hr]; assumption. Qed. +Theorem imp_iff_compat_l : forall A B C : Prop, + (B <-> C) -> ((A -> B) <-> (A -> C)). +Proof. + intros ? ? ? [Hl Hr]; split; intros H ?; [apply Hl | apply Hr]; apply H; assumption. +Qed. + +Theorem imp_iff_compat_r : forall A B C : Prop, + (B <-> C) -> ((B -> A) <-> (C -> A)). +Proof. + intros ? ? ? [Hl Hr]; split; intros H ?; [apply H, Hr | apply H, Hl]; assumption. +Qed. + +Theorem not_iff_compat : forall A B : Prop, + (A <-> B) -> (~ A <-> ~B). +Proof. + intros; apply imp_iff_compat_r; assumption. +Qed. + + (** Some equivalences *) Theorem neg_false : forall A : Prop, ~ A <-> (A <-> False). @@ -553,7 +572,8 @@ Proof. intros A P (x & Hp & Huniq); split. - intro; exists x; auto. - intros (x0 & HPx0 & HQx0) x1 HPx1. - replace x1 with x0 by (transitivity x; [symmetry|]; auto). + assert (H : x0 = x1) by (transitivity x; [symmetry|]; auto). + destruct H. assumption. Qed. |