Arguments resource_at_empty [phi] _ _.
Ltac inj_pair_tac :=
match goal with H: (@existT ?U ?P ?p ?x = @existT _ _ _ ?y) |- _ =>
generalize (@inj_pair2 U P p x y H); clear H; intro; try (subst x || subst y)
end.

Lemma resource_at_joins2:
forall phi1 phi2,
level phi1 = level phi2 ->
(forall loc, constructive_joins (phi1 @ loc) (phi2 @ loc)) ->
constructive_joins (ghost_of phi1) (ghost_of phi2) ->
joins phi1 phi2.