(* A minimal preservation property we sometimes require.*)
Definition mem_forward (m1 m2:mem) :=
(forall b, Mem.valid_block m1 b ->
Mem.valid_block m2 b /\
forall ofs p, Mem.perm m2 b ofs Max p -> Mem.perm m1 b ofs Max p).

Lemma compose_meminj_inject_incr: forall j12 j12' j23 j23'
(InjIncr12: inject_incr j12 j12') (InjIncr23: inject_incr j23 j23'),
inject_incr (compose_meminj j12 j23) (compose_meminj j12' j23').