Ltac cancel_for_forward_call ::= repeat (rewrite ?sepcon_andp_prop', ?sepcon_andp_prop);
repeat (apply andp_right; [auto; apply prop_right; auto|]); fast_cancel.
Ltac entailer_for_return ::= go_lower; entailer'.

Lemma failed_CAS_fst : forall v h h', Forall2 (failed_CAS v) h h' -> map snd h' = map snd h.