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
  ============================
   ?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'
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
Unable to unify "?x0 = ?x0" with "E.t".
Level 9: 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'
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
Unable to unify "?x0 = ?x0" with "E.t".
Level 11: 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'
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
Unable to unify "?x0 = ?x0" with "E.t".
Level 10: 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'
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
Unable to unify "?x0 = ?x0" with "E.t".
Level 9: 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'
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
Unable to unify "?x0 = ?x0" with "E.t".
Level 8: 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'
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
Unable to unify "?x0 = ?x0" with "E.t".