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 x : key × elt,
       List.In x (elements m) ->
       let
       '(k, _) := x in
        match find k m with
        | Some x0 =>
            match find k m' with
            | Some y0 => eq_elt x0 y0
            | None => False
            end
        | None => match find k m' with
                  | Some _ => False
                  | None => True
                  end
        end
  H3 : forall x : key × elt,
       List.In x (elements m') ->
       let
       '(k, _) := x in
        match find k m with
        | Some x0 =>
            match find k m' with
            | Some y0 => eq_elt x0 y0
            | None => False
            end
        | None => match find k m' with
                  | Some _ => False
                  | None => True
                  end
        end
  k : key
  k0 : key
  e : elt
  H2 : E.eq k (k0, e).1
  H4 : List.In (k0, e) (elements m')
  ============================
   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


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)