diff --git a/CHANGELOG.md b/CHANGELOG.md
index bbe665ed4eac8dbd600f4a743500c997da748d59..9a1bebc64bef8b690fc5d6cc0d0845c894c7b22c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ Coq development, but not every API-breaking change is listed. Changes marked
Changes in and extensions of the theory:
+* [#] Add new modality: ■ ("plainly").
* [#] Camera morphisms have to be homomorphisms, not just monotone functions.
* [#] A proof that `f` has a fixed point if `f^k` is contractive.
* Constructions for least and greatest fixed points over monotone predicates
diff --git a/theories/base_logic/primitive.v b/theories/base_logic/primitive.v
index 71af3c09c56ce281cbe9286998f2087a975e92d5..f251fbb1a1c7fc350c8c38497e537f418a0cf9b4 100644
--- a/theories/base_logic/primitive.v
+++ b/theories/base_logic/primitive.v
@@ -97,6 +97,9 @@ Definition uPred_wand {M} := unseal uPred_wand_aux M.
Definition uPred_wand_eq :
@uPred_wand = @uPred_wand_def := seal_eq uPred_wand_aux.
+(* Equivalently, this could be `∀ y, P n y`. That's closer to the intuition
+ of "embedding the step-indexed logic in Iris", but the two are equivalent
+ because Iris is afine. The following is easier to work with. *)
Program Definition uPred_plainly_def {M} (P : uPred M) : uPred M :=
{| uPred_holds n x := P n ε |}.
Solve Obligations with naive_solver eauto using uPred_closed, ucmra_unit_validN.
@@ -480,6 +483,8 @@ Proof.
by rewrite cmra_core_l cmra_core_idemp.
Qed.
+(* The following two laws are very similar, and indeed they hold not just for □
+ and ■, but for any modality defined as `M P n x := ∀ y, R x y → P n y`. *)
Lemma persistently_impl_plainly P Q : (■ P → □ Q) ⊢ □ (■ P → Q).
Proof.
unseal; split=> /= n x ? HPQ n' x' ????.