Module Type sound_mod (X: base_mod).
(** * Definitions  definition of Propositional Formulas*)
Inductive PropF : Set :=
| Var : PropVars -> PropF
| Bot : PropF
| Conj : PropF -> PropF -> PropF
| Disj : PropF -> PropF -> PropF
| Impl : PropF -> PropF -> PropF
.
Notation "# P" := (Var P) (at level 1) : My_scope.
Notation "A ∨ B" := (Disj A B) (at level 15, right associativity) : My_scope.
Notation "A ∧ B" := (Conj A B) (at level 15, right associativity) : My_scope.
Notation "A → B" := (Impl A B) (at level 16, right associativity) : My_scope.
Notation "⊥" := Bot (at level 0)  : My_scope.
Definition Neg A := A → ⊥.
Notation "¬ A" := (Neg A) (at level 5) : My_scope.
Definition Top := ¬⊥.
Notation "⊤" := Top (at level 0) : My_scope.
Definition BiImpl A B := (A→B)∧(B→A).
Notation "A ↔ B" := (BiImpl A B) (at level 17, right associativity) : My_scope.
(** Validness *)
(** Valuations are maps PropVars -> bool sending ⊥ to false*)
Fixpoint TrueQ v A : bool := match A with
| # P   => v P
| ⊥     => false
| B ∨ C => (TrueQ v B) || (TrueQ v C)
| B ∧ C => (TrueQ v B) && (TrueQ v C)
| B → C => (negb (TrueQ v B)) || (TrueQ v C)
end.
Definition Satisfies v Γ := forall A, In A Γ -> Is_true (TrueQ v A).
Definition Models Γ A := forall v,Satisfies v Γ->Is_true (TrueQ v A).
Notation "Γ ⊨ A" := (Models Γ A) (at level 80).
Definition Valid A := [] ⊨ A.
(** Provability *)
Reserved Notation "Γ ⊢ A" (at level 80).
Inductive Nc : list PropF-> PropF->Prop :=
| Nax   : forall Γ A  ,    In A Γ                           -> Γ ⊢ A
| ImpI  : forall Γ A B,  A::Γ ⊢ B                           -> Γ ⊢ A → B
| ImpE  : forall Γ A B,     Γ ⊢ A → B -> Γ ⊢ A              -> Γ ⊢ B
| BotC  : forall Γ A  , ¬A::Γ ⊢ ⊥                              -> Γ ⊢ A
| AndI  : forall Γ A B,     Γ ⊢ A     -> Γ ⊢ B              -> Γ ⊢ A∧B
| AndE1 : forall Γ A B,     Γ ⊢ A∧B                        -> Γ ⊢ A
| AndE2 : forall Γ A B,     Γ ⊢ A∧B                        -> Γ ⊢ B
| OrI1  : forall Γ A B,     Γ ⊢ A                           -> Γ ⊢ A∨B
| OrI2  : forall Γ A B,     Γ ⊢ B                           -> Γ ⊢ A∨B
| OrE   : forall Γ A B C,   Γ ⊢ A∨B -> A::Γ ⊢ C -> B::Γ ⊢ C -> Γ ⊢ C
where "Γ ⊢ A" := (Nc Γ A) : My_scope.
Definition Provable A := [] ⊢ A.
(**The Theorems we are going to prove*)
Definition Prop_Soundness := forall A,Provable A->Valid A.
Definition Prop_Completeness := forall A,Valid A->Provable A.
(** * Theorems *)
Ltac mp := eapply ImpE.
Ltac AddnilL := match goal with
| |- _ ?Γ _ => change Γ with ([]++Γ)
end.
Ltac in_solve := intros;repeat
(eassumption
||match goal with
| H:In _ (_::_) |- _ => destruct H;[subst;try discriminate|]
| H:In _ (_++_) |- _ => apply in_app_iff in H as [];subst
| |- In _ (_++_) => apply in_app_iff;(left;in_solve;fail)||(right;in_solve;fail)
end
||(once constructor;reflexivity)
||constructor 2).
Ltac is_ass := once econstructor;in_solve.
Ltac case_bool v A := let HA := fresh "H" in
(case_eq (TrueQ v A);intro HA;try rewrite HA in *;simpl in *;try trivial;try contradiction).
Local Ltac prove_satisfaction :=
intros ? K;destruct K;[subst;simpl;
match goal with
| [ H : TrueQ _ _ = _  |-  _ ] => rewrite H
end;exact I|auto].
induction x;destruct y;try (right;discriminate);
try (destruct (IHx1 y1);[destruct (IHx2 y2);[left;f_equal;assumption|]|];
right;injection;intros;contradiction).
destruct (Varseq_dec p p0).
left;f_equal;assumption.
right;injection;intro;contradiction.
left;reflexivity.
Qed.

Lemma Excluded_Middle : forall Γ A, Γ ⊢ A∨¬A.