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'
  k0 : key
  H1 : match find k0 m with
       | Some x =>
           match find k0 m' with
           | Some y => eq_elt x y
           | None => False
           end
       | None => match find k0 m' with
                 | Some _ => False
                 | None => True
                 end
       end
  H3 : forall (k : key) (e : elt),
       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
  k : key
  e : elt
  H2 : E.eq k k0
  H4 : List.In (k0, e) (elements m)
  H5 : forall k : key, find k m' = find k m'
  H6 : forall k : key, find k m = find k m
  ============================
   ?T0


DEBUG:Going to execute:
let H := open_constr:((H _)) in
           guarded_specialize_term_under_binders_by' guard_tac H tac
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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 13: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 16: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 16: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 15: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 14: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 13: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").
Level 12: 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'
k0 : key
H1 : match find k0 m with
     | Some x =>
         match find k0 m' with
         | Some y => eq_elt x y
         | None => False
         end
     | None => match find k0 m' with
               | Some _ => False
               | None => True
               end
     end
H3 : forall (k : key) (e : elt),
     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
k : key
e : elt
H2 : E.eq k k0
H4 : List.In (k0, e) (elements m)
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H4" has type "List.In (k0, e) (elements m)"
while it is expected to have type "List.In (?k, ?e) (elements m')"
(cannot unify "m" and "m'").