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(** Author: Cristina Cornes From : Constructing Recursion Operators in Type Theory L. Paulson  JSC (1986) 2, 325-355 *)
Section Wf_Disjoint_Union.
Variables A B : Type.
Variable leA : A -> A -> Prop.
Variable leB : B -> B -> Prop.
Notation Le_AsB := (le_AsB A B leA leB).

Lemma acc_A_sum : forall x:A, Acc leA x -> Acc Le_AsB (inl B x).