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
  ============================
   ?T0


DEBUG:Going to execute:
fun guard_tac H tac =>
             lazymatch type of H with
             | forall a, _ =>
                 match goal with
                 | _ =>
                     let __ := lazymatch goal with
                               | _ => guard_tac H
                               end in
                     open_constr:((H ltac:((progress tac))))
                 | _ =>
                     let H := open_constr:((H _)) in
                     guarded_specialize_term_under_binders_by' guard_tac H
                      tac
                 end
             end