add some TODO so some stuff does not get forgotten

algebra/dra.v

@@ -127,6 +127,7 @@ Lemma to_validity_op (x y : A) :
   to_validity (x ⋅ y) ≡ to_validity x ⋅ to_validity y.
 Proof. split; naive_solver auto using dra_op_valid. Qed.
 
+(* TODO: This has to be proven again. *)
 (*
 Lemma to_validity_included x y:
   (✓ y ∧ to_validity x ≼ to_validity y)%C ↔ (✓ x ∧ x ≼ y).

algebra/sts.v

@@ -385,6 +385,7 @@ Qed.
 (* This is surprisingly different from to_validity_included. I am not sure
    whether this is because to_validity_included is non-canonical, or this
    one here is non-canonical - but I suspect both. *)
+(* TODO: These have to be proven again. *)
 (*
 Lemma sts_frag_included S1 S2 T1 T2 :
   closed S2 T2 → S2 ≢ ∅ →