Definition memory_block (sh: share) (n: Z) (v: val) : mpred :=
match v with
| Vptr b ofs => (!!(Ptrofs.unsigned ofs + n < Ptrofs.modulus)) && memory_block' sh (nat_of_Z n) b (Ptrofs.unsigned ofs)
| _ => FF
end.

Lemma mapsto_share_join:
forall sh1 sh2 sh t p v,
join sh1 sh2 sh ->
mapsto sh1 t p v * mapsto sh2 t p v = mapsto sh t p v.