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
  k : key
  H4 : 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
  e : elt
  e' : elt
  H2 : find k m = Some e
  H3 : find k m' = Some e'
  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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (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'
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
k : key
H4 : 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
e, e' : elt
H2 : find k m = Some e
H3 : find k m' = Some e'
H5 : forall k : key, find k m' = find k m'
H6 : forall k : key, find k m = find k m
The term "H3" has type "find k m' = Some e'"
while it is expected to have type "find k m = Some ?e" (cannot unify 
"m'" and "m").