Goal:
  
  A : Type
  B : Type
  a : A
  l : list A
  f : A → B
  g : A → B
  IHl : map f l = map g l → Forall (λ x : A, f x = g x) l
  Ha : f a = g a
  Hl : map f l = map g l
  ============================
   (Forall (λ x : A, f x = g x) (a :: l))


DEBUG:Going to execute:
constructor
Level 0: Backtrace:

No matching clauses for match.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.