Proof using overlay_map_congr name_map_bijective.
move => h m failed ns ns' H_nd H_pm.
apply NoDup_Permutation; last split.
- apply (@nodup_tot_map m); first exact: in_map2snd_snd.
apply NoDup_map2snd.
by apply NoDup_remove_all.
- apply NoDup_map2snd.
apply NoDup_remove_all.
move: H_pm.
apply: NoDup_Permutation_NoDup.
exact: nodup_to_map_name.
- case: x => n m' H_in.
have H_eq := tot_map_in_snd _ _ _ _ H_in.
rewrite /= in H_eq.
rewrite H_eq in H_in.
rewrite H_eq {H_eq}.
apply in_tot_map_name in H_in.
apply in_map2snd_related_in in H_in.
move: H_in => [H_adj H_in].
apply in_failed_exclude in H_in.
move: H_in => [H_in H_in'].
have H_nin: ~ In n (map tot_map_name failed).
rewrite -(tot_map_name_inverse_inv n).
exact: not_in_failed_not_in.
apply tot_adjacent_to_fst_snd in H_adj.
rewrite tot_map_name_inverse_inv in H_adj.
have H_inn: In n ns'.
apply (Permutation_in n) in H_pm => //.
rewrite -(tot_map_name_inverse_inv n).
exact: in_failed_in.
exact: in_in_adj_map_pair.
exact: in_map2snd_snd.
- case: x => n m' H_in.
have H_eq := in_map2snd_snd _ _ adjacent_to adjacent_to_dec _ _ _ _ H_in.
rewrite /= in H_eq.
rewrite H_eq.
rewrite H_eq in H_in.
apply in_map2snd_related_in in H_in.
move: H_in => [H_adj H_in].
rewrite -(tot_map_name_inverse_inv n) in H_adj.
apply tot_adjacent_to_fst_snd in H_adj.
apply in_exclude_not_in_failed_map in H_in.
move: H_in => [H_in_f H_in].
apply not_in_map_not_in_failed in H_in_f.
have H_in_n: In (tot_map_name_inv n) ns.
apply Permutation_sym in H_pm.
apply (Permutation_in n) in H_pm => //.
apply: tot_map_name_in.
by rewrite tot_map_name_inverse_inv.
apply in_tot_map_msg; first by move => nm; apply in_map2snd_snd.
apply: adjacent_in_in_msg => //.
exact: not_in_failed_in_exclude.
Qed.

Lemma map_map_pair_eq :
forall h m failed,
Permutation
(map (fun nm : name * msg => (tot_map_name (fst nm), tot_map_msg (snd nm))) (map2snd m (filter_rel adjacent_to_dec h (remove_all name_eq_dec failed nodes))))
(map2snd (tot_map_msg m) (filter_rel adjacent_to_dec (tot_map_name h) (remove_all name_eq_dec (map tot_map_name failed) nodes))).