Goal:
  
  A : Type
  B : Type
  f : A → B
  g : A → B
  x : A
  l : list A
  p : f x = g x
  X : All (λ x : A, f x = g x) l
  IHX : map f l = map g l
  ============================
   (g x :: map g l = g x :: map g l)


DEBUG:Going to execute:
solve [ do_atom | use_hyps; do_ccl ]