Goal:
  
  A : Type
  B : Type
  map_InP : ∀ l : list A, (∀ x : A, In x l → B) → list B
  x0 : A
  xs : list A
  f : ∀ x : A, In x (x0 :: xs) → B
  x : A
  inx : In x xs
  ============================
   (x0 = x ∨ In x xs)


DEBUG:Going to execute:
try typeclasses eauto  10 with program
Level 0: Backtrace:

No head constant to reduce.
Level 0: Backtrace:

No head constant to reduce.
Level 0: Backtrace:

No head constant to reduce.
Level 0: Backtrace:

No head constant to reduce.
Level 0: Backtrace:

No head constant to reduce.
Level 0: Backtrace:

No applicable tactic.