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:
let H := open_constr:((H _)) in
           guarded_specialize_term_under_binders_by' guard_tac H tac
DEBUG LTAC Evaluated term: eq_refl
Level 0: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".
Level 5: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".
Level 7: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".
Level 6: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".
Level 5: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".
Level 4: Backtrace:

In environment
elt : Type
eq_elt : elt -> elt -> Prop
m, 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
Unable to unify "?x = ?x" with "E.t".