Proof of unicity of proofs for:

 1. decidable equalities
 2. P x = true for some function P

diff --git a/helm/matita/library/datatypes/bool.ma b/helm/matita/library/datatypes/bool.ma
index a223d7d0c9333c27b77e328b253e19229fe319f1..a4667da30249730b98bc4f39c522dd824a180019 100644 (file)
--- a/helm/matita/library/datatypes/bool.ma
+++ b/helm/matita/library/datatypes/bool.ma
@@ -84,3 +84,26 @@ match b with
 | false  \Rightarrow Q].
 
 (*CSC: missing notation for if_then_else *)
+
+theorem bool_to_decidable_eq:
+ \forall b1,b2:bool. decidable (b1=b2).
+ intros.
+ unfold decidable.
+ elim b1.
+  elim b2.
+   left. reflexivity.
+   right. exact not_eq_true_false.
+  elim b2.
+   right. unfold Not. intro.
+   apply not_eq_true_false.
+   symmetry. exact H.
+   left. reflexivity.
+qed.
+
+theorem P_x_to_P_x_to_eq:
+ \forall A:Set. \forall P: A \to bool.
+  \forall x:A. \forall p1,p2:P x = true. p1 = p2.
+ intros.
+ apply eq_to_eq_to_eq_p_q.
+ exact bool_to_decidable_eq.
+qed. 

diff --git a/helm/matita/library/logic/connectives.ma b/helm/matita/library/logic/connectives.ma
index a8cba2b4a394f15584f779fc7749d713a94ad694..2848c08c5753086d5ffb5e9073c1b2687ee95bae 100644 (file)
--- a/helm/matita/library/logic/connectives.ma
+++ b/helm/matita/library/logic/connectives.ma
@@ -56,7 +56,21 @@ inductive Or (A,B:Prop) : Prop \def
 (*CSC: the URI must disappear: there is a bug now *)
 interpretation "logical or" 'or x y =
   (cic:/matita/logic/connectives/Or.ind#xpointer(1/1) x y).
-   
+
+theorem Or_ind':
+ \forall A,B:Prop.
+  \forall P: A \lor B \to Prop.
+   (\forall p:A. P (or_introl ? ? p)) \to
+   (\forall q:B. P (or_intror ? ? q)) \to
+    \forall p:A \lor B. P p.
+ intros.
+ apply
+  ([\lambda p.P p]
+   match p with
+    [(or_introl p) \Rightarrow H p
+    |(or_intror q) \Rightarrow H1 q]).
+qed.
+
 definition decidable : Prop \to Prop \def \lambda A:Prop. A \lor \lnot A.
 
 inductive ex (A:Type) (P:A \to Prop) : Prop \def

diff --git a/helm/matita/library/logic/equality.ma b/helm/matita/library/logic/equality.ma
index ed257afa4c3e47c8e6017ee412f38ac97ef6cea1..70ade5589c46f0eb073a7d991d41dd7a19ab2eaa 100644 (file)
--- a/helm/matita/library/logic/equality.ma
+++ b/helm/matita/library/logic/equality.ma
@@ -27,6 +27,16 @@ interpretation "leibnitz's non-equality"
   'neq x y = (cic:/matita/logic/connectives/Not.con
     (cic:/matita/logic/equality/eq.ind#xpointer(1/1) _ x y)).
 
+theorem eq_ind':
+ \forall A. \forall x:A. \forall P: \forall y:A. x=y \to Prop.
+  P ? (refl_eq ? x) \to \forall y:A. \forall p:x=y. P y p.
+ intros.
+ exact
+  ([\lambda y:A. \lambda p:eq A x y.P y p]
+   match p with
+    [refl_eq \Rightarrow H]).
+qed.
+ 
 theorem reflexive_eq : \forall A:Type. reflexive A (eq A).
 simplify.intros.apply refl_eq.
 qed.
@@ -69,6 +79,124 @@ x1=x2 \to y1=y2 \to f x1 y1 = f x2 y2.
 intros.elim H1.elim H.reflexivity.
 qed.
 
+definition comp \def
+ \lambda A.
+  \lambda x,y,y':A.
+   \lambda eq1:x=y.
+    \lambda eq2:x=y'.
+     eq_ind ? ? (\lambda a.a=y') eq2 ? eq1.
+     
+lemma trans_sym_eq:
+ \forall A.
+  \forall x,y:A.
+   \forall u:x=y.
+    comp ? ? ? ? u u = refl_eq ? y.
+ intros.
+ apply (eq_ind' ? ? ? ? ? u).
+ reflexivity.
+qed.
+
+definition nu \def
+ \lambda A.
+  \lambda H: \forall x,y:A. decidable (x=y).
+   \lambda x,y. \lambda p:x=y.
+     match H x y with
+      [ (or_introl p') \Rightarrow p'
+      | (or_intror K) \Rightarrow False_ind ? (K p) ].
+
+theorem nu_constant:
+ \forall A.
+  \forall H: \forall x,y:A. decidable (x=y).
+   \forall x,y:A.
+    \forall u,v:x=y.
+     nu ? H ? ? u = nu ? H ? ? v.
+ intros.
+ unfold nu.
+ unfold decidable in H.
+ apply (Or_ind' ? ? ? ? ? (H x y)); simplify.
+  intro; reflexivity.
+  intro; elim (q u).
+qed.
+
+definition nu_inv \def
+ \lambda A.
+  \lambda H: \forall x,y:A. decidable (x=y).
+   \lambda x,y:A.
+    \lambda v:x=y.
+     comp ? ? ? ? (nu ? H ? ? (refl_eq ? x)) v.
+
+theorem nu_left_inv:
+ \forall A.
+  \forall H: \forall x,y:A. decidable (x=y).
+   \forall x,y:A.
+    \forall u:x=y.
+     nu_inv ? H ? ? (nu ? H ? ? u) = u.
+ intros.
+ apply (eq_ind' ? ? ? ? ? u).
+ unfold nu_inv.
+ apply trans_sym_eq.
+qed.
+
+theorem eq_to_eq_to_eq_p_q:
+ \forall A. \forall x,y:A.
+  (\forall x,y:A. decidable (x=y)) \to
+   \forall p,q:x=y. p=q.
+ intros.
+ rewrite < (nu_left_inv ? H ? ? p).
+ rewrite < (nu_left_inv ? H ? ? q).
+ elim (nu_constant ? H ? ? q).
+ reflexivity.
+qed.
+
+(*CSC: alternative proof that does not pollute the environment with
+  technical lemmata. Unfortunately, it is a pain to do without proper
+  support for let-ins.
+theorem eq_to_eq_to_eq_p_q:
+ \forall A. \forall x,y:A.
+  (\forall x,y:A. decidable (x=y)) \to
+   \forall p,q:x=y. p=q.
+intros.
+letin nu \def
+ (\lambda x,y. \lambda p:x=y.
+   match H x y with
+    [ (or_introl p') \Rightarrow p'
+    | (or_intror K) \Rightarrow False_ind ? (K p) ]).
+cut
+ (\forall q:x=y.
+   eq_ind ? ? (\lambda z. z=y) (nu ? ? q) ? (nu ? ? (refl_eq ? x))
+   = q).
+focus 8.
+ clear q; clear p.
+ intro.
+ apply (eq_ind' ? ? ? ? ? q);
+ fold simplify (nu ? ? (refl_eq ? x)).
+ generalize in match (nu ? ? (refl_eq ? x)); intro.
+ apply
+  (eq_ind' A x
+   (\lambda y. \lambda u.
+    eq_ind A x (\lambda a.a=y) u y u = refl_eq ? y)
+   ? x H1).
+ reflexivity.
+unfocus.
+rewrite < (Hcut p); fold simplify (nu ? ? p).
+rewrite < (Hcut q); fold simplify (nu ? ? q).
+apply (Or_ind' (x=x) (x \neq x)
+ (\lambda p:decidable (x=x). eq_ind A x (\lambda z.z=y) (nu x y p) x
+   ([\lambda H1.eq A x x]
+    match p with
+    [(or_introl p') \Rightarrow p'
+    |(or_intror K) \Rightarrow False_ind (x=x) (K (refl_eq A x))]) =
+   eq_ind A x (\lambda z.z=y) (nu x y q) x
+    ([\lambda H1.eq A x x]
+     match p with
+    [(or_introl p') \Rightarrow p'
+    |(or_intror K) \Rightarrow False_ind (x=x) (K (refl_eq A x))]))
+ ? ? (H x x)).
+intro; simplify; reflexivity.
+intro q; elim (q (refl_eq ? x)).
+qed.
+*)
+
 (*
 theorem a:\forall x.x=x\land True.
 [