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 (k : key) (e : elt),
       List.In (k, e) (elements m') ->
       let
       '(k0, _) := (k, e) in
        match find k0 m with
        | Some x =>
            match find k0 m' with
            | Some y0 => eq_elt x y0
            | None => False
            end
        | None => match find k0 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:
fun all_ways guard_tac H tac =>
             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)