Proof using.
elim => [|n l IH] failed n' h; first by rewrite remove_all_nil.
have H_cn := remove_all_cons name_eq_dec failed n l.
break_or_hyp; break_and; find_rewrite; first exact: IH.
rewrite /=.
case (adjacent_to_dec _ _) => /= H_dec'.
move => H_in.
case: H_in => H_in.
rewrite {1}H_in -{4}H_in.
split => //.
by left.
apply IH in H_in.
move: H_in => [H_eq H_in].
split => //.
by right.
move => H_in.
apply IH in H_in.
move: H_in => [H_eq H_in].
split => //.
by right.
Qed.

Lemma in_failed_exclude :
forall ns failed n,
In (tot_map_name_inv n) (remove_all name_eq_dec failed ns) ->
~ In (tot_map_name_inv n) failed /\ In (tot_map_name_inv n) ns.