End DECIDABLE_PREDICATE.
(** * Well-founded orderings *)
(** A non-dependent version of lexicographic ordering. *)
Section LEX_ORDER.
Variable A: Type.
Variable B: Type.
Variable ordA: A -> A -> Prop.
Variable ordB: B -> B -> Prop.
Inductive lex_ord: A*B -> A*B -> Prop :=
| lex_ord_left: forall a1 b1 a2 b2,
ordA a1 a2 -> lex_ord (a1,b1) (a2,b2)
| lex_ord_right: forall a b1 b2,
ordB b1 b2 -> lex_ord (a,b1) (a,b2).

Lemma wf_lex_ord:
well_founded ordA -> well_founded ordB -> well_founded lex_ord.