Goal:
  
  A : Type
  B : Type
  f : A → B
  a : A
  l : list A
  p : B → bool
  IHl : ∀ (f : A → B) (p : B → bool),
          forallb p (map f l) = forallb (λ x : A, p (f x)) l
  ============================
   (p (f a) && forallb p (map f l) = p (f a) && forallb (λ x : A, p (f x)) l)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 2: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".
Level 2: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".
Level 3: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".
Level 3: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".
Level 2: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".
Level 2: Backtrace:

In environment
A : Type
B : Type
f : A → B
a : A
l : list A
p : B → bool
IHl : ∀ (f : A → B) (p : B → bool),
        forallb p (map f l) = forallb (λ x : A, p (f x)) l
Unable to unify "p (f a) && forallb (λ x : A, p (f x)) l" with
 "p (f a) && forallb p (map f l)".