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,
       (exists 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,
       (exists 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:
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