Goal:
  
  A : Type
  B : Type
  a : A
  l : list A
  f : A -> option B
  g : A -> option B
  x : list B
  Hfg : forall (x : A) (y : B), f x = Some y -> g x = Some y
  b : B
  fa : f a = Some b
  l0 : list B
  H' : map_option_out (map g l) = Some l0
  ============================
   (Some (b :: l0) = Some x -> Some (b :: l0) = Some x)


DEBUG:Going to execute:
<coq-core.plugins.cc::cc@0> $1
DEBUG LTAC Evaluated term: H'
DEBUG LTAC Evaluated term: H'