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) (y : key × elt),
          (E.eq k y.1 /\ e = y.2) /\ List.In y (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
  H3 : forall k : key,
       (exists (e : elt) (y : key × elt),
          (E.eq k y.1 /\ e = y.2) /\ List.In y (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
  k : key
  e : elt
  H2 : List.In (k, 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 ident funl funr tac =>
             repeat
              match goal with
              | H:context p[ ident ]
                |- _ =>
                    let H0 := context p [ funl ] in
                    let H1 := context p [ funr ] in
                    let H0' := eval cbv beta in H0 in
                    let H1' := eval cbv beta in H1 in
                    assert H0' by tac H; assert H1' by tac H; clear H
              end