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] *)

Theorem perm_drop_4:
forall b' ofs k p', perm m' b' ofs k p' -> perm m b' ofs k p'.