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'
  H3 : forall (k : key) (e e' : elt),
       find k m = Some e -> find k m' = Some e' -> eq_elt e e'
  k : key
  x : elt
  H1 : find k m = Some x
  H4 : forall (k : key) (e : elt),
       find k m = Some e -> exists e0 : elt, find k m' = Some e0
  H5 : forall (k : key) (e : elt),
       find k m' = Some e -> exists e0 : elt, find k m = Some e0
  ============================
   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:
lazymatch x with
           | let a := ?b in ?f => constr:(match b with
                                          | a => f
                                          end)
           end
DEBUG LTAC Evaluated term: (let H2 : forall k : key, find k m' = find k m' :=
                              fun k : key => H0 k k (E.eq_refl k) in
                            H2)
DEBUG LTAC Evaluated term: (let H2 : forall k : key, find k m' = find k m' :=
                              fun k : key => H0 k k (E.eq_refl k) in
                            H2)