Goal:
  
  elt : Type
  eq_elt : elt -> elt -> Prop
  m : t elt
  m' : t elt
  H : forall x y : key, E.eq x y -> find x m = find y m
  H0 : forall x y : key, E.eq x y -> find x m' = find y m'
  H1 : forall (k : key) (e : elt),
       find k m = Some e ->
       match find k m with
       | Some x =>
           match find k m' with
           | Some y => eq_elt x y
           | None => False
           end
       | None => match find k m' with
                 | Some _ => False
                 | None => True
                 end
       end
  H3 : forall (k : key) (e : elt),
       find k m' = Some e ->
       match find k m with
       | Some x =>
           match find k m' with
           | Some y => eq_elt x y
           | None => False
           end
       | None => match find k m' with
                 | Some _ => False
                 | None => True
                 end
       end
  k : key
  x : elt
  H2 : find k m' = Some x
  ============================
   (exists e : elt, find k m = Some e)


DEBUG:Going to execute:
idtac;
            (let is_transparent :=
              match goal with
              | _ => let __ := eval cbv delta [H] in H in
                     constr:(true)
              | _ => constr:(false)
              end
             in
             lazymatch constr:((all_ways, is_transparent))
             with
             | (false, true) =>
                 let H' := fresh in
                 rename H into H';
                  (let H'' :=
                    guarded_specialize_term_under_binders_by guard_tac H' tac
                   in
                   pose (H := H''); subst H')
             | (true, true) =>
                 let H :=
                  guarded_specialize_term_under_binders_by guard_tac H tac
                 in
                 unique
                 pose
                 H
             | (false, false) =>
                 let H :=
                  guarded_specialize_term_under_binders_by guard_tac H tac
                 in
                 specialize
                 H
             | (true, false) =>
                 let H :=
                  guarded_specialize_term_under_binders_by guard_tac H tac
                 in
                 unique
                 pose
                 proof
                 H
             end)