comment update

set.mm

@@ -46709,7 +46709,8 @@ although the definition does not require it (see ~ dfid2 for a case
     $( Change first bound variable in an ordered-pair class abstraction, using
        explicit substitution.  (Contributed by NM, 6-Oct-2004.)  (Revised by
        Mario Carneiro, 14-Oct-2016.)  Add disjoint variable condition to avoid
-       ~ ax-13 .  (Revised by Gino Giotto, 17-Jan-2024.) $)
+       ~ ax-13 .  See ~ cbvopab1g for a less restrictive version requiring more
+       axioms.  (Revised by Gino Giotto, 17-Jan-2024.) $)
     cbvopab1 $p |- { <. x , y >. | ph } = { <. z , y >. | ps } $=
       ( vw vv cv cop wceq wa wex cab copab nfv nfan nfex wsb nfs1v opeq1 eqeq2d
       sbequ12 anbi12d exbidv cbvexv1 nfsbv sbhypf bitri abbii df-opab 3eqtr4i )