Goal:
  
  A : Type
  forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
  x0 : A
  xs : list A
  H : ∀ x : A, In x (x0 :: xs) → bool
  x : A
  inx : In x xs
  ============================
   (x0 = x ∨ In x xs)


DEBUG:Going to execute:
match H with
           | H' => fail 2
           | _ => unify X Y; clear H' || clear H
           end
Level 4: Backtrace:

In environment
A : Type
forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
x0 : A
xs : list A
H : ∀ x : A, In x (x0 :: xs) → bool
x : A
inx : In x xs
Unable to unify "∀ x : A, In x (x0 :: xs) → bool" with 
"A".
Level 4: Backtrace:

In environment
A : Type
forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
x0 : A
xs : list A
H : ∀ x : A, In x (x0 :: xs) → bool
x : A
inx : In x xs
Unable to unify "∀ x : A, In x (x0 :: xs) → bool" with 
"A".
Level 4: Backtrace:

In environment
A : Type
forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
x0 : A
xs : list A
H : ∀ x : A, In x (x0 :: xs) → bool
x : A
inx : In x xs
Unable to unify "∀ x : A, In x (x0 :: xs) → bool" with 
"A".
Level 4: Backtrace:

In environment
A : Type
forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
x0 : A
xs : list A
H : ∀ x : A, In x (x0 :: xs) → bool
x : A
inx : In x xs
Unable to unify "∀ x : A, In x (x0 :: xs) → bool" with 
"A".
Level 3: Backtrace:

In environment
A : Type
forallb_InP : ∀ l : list A, (∀ x : A, In x l → bool) → bool
x0 : A
xs : list A
H : ∀ x : A, In x (x0 :: xs) → bool
x : A
inx : In x xs
Unable to unify "∀ x : A, In x (x0 :: xs) → bool" with 
"A".