Definition mapsto x v : pred := fun m => forall n, m n = if eq_nat_dec x n then Some v else None.Definition mapsto_ x : pred := fun m => forall n, if eq_nat_dec x n then m n <> None else m n = None.

Lemma precise_join R m1 m2 : precise R -> m1 |= R -> m2 |= R -> joins m1 m2 -> empty m1 /\ empty m2.