Inductive prod_3 (A B C : Set) : Set :=
    triplet : A -> B -> C -> prod_3 A B C.Inductive prod_3 (A B C : Set) : Set :=
    triplet : A -> B -> C -> prod_3 A B C.

(* Specifications: *)
Theorem fst_3 : prod_3 A B C -> A.
Theorem snd_3 : prod_3 A B C -> B.
Theorem thd_3 : prod_3 A B C -> C.