Section sec_exteq.
Variable T: Type.
CoInductive exteq : infseq T -> infseq T -> Prop :=
exteq_intro :
forall x s1 s2, exteq s1 s2 -> exteq (Cons x s1) (Cons x s2).

Lemma exteq_inversion :
forall (x1:T) s1 x2 s2,
exteq (Cons x1 s1) (Cons x2 s2) -> x1 = x2 /\ exteq s1 s2.