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+(* Not having a [return] clause causes the [refine] at the bottom to stack overflow before f65fa9de8a4c9c12d933188a755b51508bd51921 *)
+
+Require Import Coq.Lists.List.
+Require Import Relations RelationClasses.
+
+Set Implicit Arguments.
+Set Strict Implicit.
+Set Asymmetric Patterns.
+
+Section hlist.
+  Context {iT : Type}.
+  Variable F : iT -> Type.
+
+  Inductive hlist : list iT -> Type :=
+  | Hnil  : hlist nil
+  | Hcons : forall l ls, F l -> hlist ls -> hlist (l :: ls).
+
+  Definition hlist_hd {a b} (hl : hlist (a :: b)) : F a :=
+    match hl in hlist x return match x with
+                                 | nil => unit
+                                 | l :: _ => F l
+                               end with
+      | Hnil => tt
+      | Hcons _ _ x _ => x
+    end.
+
+  Definition hlist_tl {a b} (hl : hlist (a :: b)) : hlist b :=
+    match hl in hlist x return match x with
+                                 | nil => unit
+                                 | _ :: ls => hlist ls
+                               end with
+      | Hnil => tt
+      | Hcons _ _ _ x => x
+    end.
+
+  Lemma hlist_eta : forall ls (h : hlist ls),
+    h = match ls as ls return hlist ls -> hlist ls with
+          | nil => fun _ => Hnil
+          | a :: b => fun h => Hcons (hlist_hd h) (hlist_tl h)
+        end h.
+  Proof.
+    intros. destruct h; auto.
+  Qed.
+
+  Variable eqv : forall x, relation (F x).
+
+  Inductive equiv_hlist : forall ls, hlist ls -> hlist ls -> Prop :=
+  | hlist_eqv_nil : equiv_hlist Hnil Hnil
+  | hlist_eqv_cons : forall l ls x y h1 h2, eqv x y -> equiv_hlist h1 h2 ->
+                                            @equiv_hlist (l :: ls) (Hcons x h1) (Hcons y h2).
+
+  Global Instance Reflexive_equiv_hlist (R : forall t, Reflexive (@eqv t)) ls
+  : Reflexive (@equiv_hlist ls).
+  Proof.
+    red. induction x; constructor; auto. reflexivity.
+  Qed.
+
+  Global Instance Transitive_equiv_hlist (R : forall t, Transitive (@eqv t)) ls
+  : Transitive (@equiv_hlist ls).
+  Proof.
+    red. induction 1.
+    { intro; assumption. }
+    { rewrite (hlist_eta z).
+      Timeout 2 Fail refine
+        (fun H =>
+           match H in @equiv_hlist ls X Y
+                 return
+                 (* Uncommenting the following gives an immediate error in 8.4pl3; commented out results in a stack overflow *)
+                 match ls (*as ls return hlist ls -> hlist ls -> Type*) with
+                   | nil => fun _ _ : hlist nil => True
+                   | l :: ls => fun (X Y : hlist (l :: ls)) =>
+                                  equiv_hlist (Hcons x h1) Y
+                 end X Y
+           with
+             | hlist_eqv_nil => I
+             | hlist_eqv_cons l ls x y h1 h2 pf pf' =>
+               _
+           end).