End FREE.
Local Hint Resolve valid_block_free_1 valid_block_free_2
perm_free_1 perm_free_2 perm_free_3
valid_access_free_1 valid_access_free_inv_1: mem.
(** ** Properties related to [drop_perm] *)

Lemma valid_access_drop_1:
forall chunk b' ofs p',
b' <> b \/ ofs + size_chunk chunk <= lo \/ hi <= ofs \/ perm_order p p' ->
valid_access m chunk b' ofs p' -> valid_access m' chunk b' ofs p'.