+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| A.Asperti, C.Sacerdoti Coen, *)
+(* ||A|| E.Tassi, S.Zacchiroli *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU Lesser General Public License Version 2.1 *)
+(* *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/datatypes/constructors/".
+include "logic/equality.ma".
+
+inductive void : Set \def.
+
+inductive Prod (A,B:Set) : Set \def
+pair : A \to B \to Prod A B.
+
+definition fst \def \lambda A,B:Set.\lambda p: Prod A B.
+match p with
+[(pair a b) \Rightarrow a].
+
+definition snd \def \lambda A,B:Set.\lambda p: Prod A B.
+match p with
+[(pair a b) \Rightarrow b].
+
+theorem eq_pair_fst_snd: \forall A,B:Set.\forall p: Prod A B.
+p = pair A B (fst A B p) (snd A B p).
+intros.elim p.simplify.reflexivity.
+qed.
+
+inductive Sum (A,B:Set) : Set \def
+ inl : A \to Sum A B
+| inr : B \to Sum A B.