Goal:
  
  A : Type
  B : Type
  f : A → B
  a : A
  l : list A
  H : a :: l ≠ []
  e : map f (a :: l) = []
  ============================
   (a :: l = [])


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

No such contradiction
Level 0: Backtrace:

No such contradiction