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diff --git a/test-suite/bugs/opened/4728.v b/test-suite/bugs/opened/4728.v
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+(*I'd like the final [Check] in the following to work:*)
+
+Ltac fin_eta_expand :=
+  [ > lazymatch goal with
+      | [ H : _ |- _ ] => clear H
+      end..
+  | lazymatch goal with
+    | [ H : ?T |- ?T ]
+      => exact H
+    | [ |- ?G ]
+      => fail 0 "No hypothesis matching" G
+    end ];
+  let n := numgoals in
+  tryif constr_eq numgoals 0
+  then idtac
+  else fin_eta_expand.
+
+Ltac pre_eta_expand x :=
+  let T := type of x in
+  let G := match goal with |- ?G => G end in
+  unify T G;
+  unshelve econstructor;
+  destruct x;
+  fin_eta_expand.
+
+Ltac eta_expand x :=
+  let v := constr:(ltac:(pre_eta_expand x)) in
+  idtac v;
+  let v := (eval cbv beta iota zeta in v) in
+  exact v.
+
+Notation eta_expand x := (ltac:(eta_expand x)) (only parsing).
+
+Ltac partial_unify eqn :=
+  lazymatch eqn with
+  | ?x = ?x => idtac
+  | ?f ?x = ?g ?y
+    => partial_unify (f = g);
+       (tryif unify x y then
+           idtac
+         else tryif has_evar x then
+             unify x y
+           else tryif has_evar y then
+               unify x y
+             else
+               idtac)
+  | ?x = ?y
+    => idtac;
+       (tryif unify x y then
+           idtac
+         else tryif has_evar x then
+             unify x y
+           else tryif has_evar y then
+               unify x y
+             else
+               idtac)
+  end.
+
+Tactic Notation "{" open_constr(old_record) "with" open_constr(new_record) "}" :=
+  let old_record' := eta_expand old_record in
+  partial_unify (old_record = new_record);
+  eexact new_record.
+
+Set Implicit Arguments.
+Record prod A B := pair { fst : A ; snd : B }.
+Infix "*" := prod : type_scope.
+Notation "( x , y , .. , z )" := (pair .. (pair x y) .. z) : core_scope.
+
+Notation "{ old 'with' new }" := (ltac:({ old with new })) (only parsing).
+
+Check ltac:({ (1, 1) with {| snd := 2 |} }).
+Fail Check { (1, 1) with {| snd := 2 |} }. (* Error: Cannot infer this placeholder of type "Type"; should succeed *)