Goal:
  
  G : t
  A : Type
  B : Type
  C : Type
  f : A -> B -> A
  g : A -> C -> A
  h : C -> B
  l' : list C
  acc : A
  hfg : forall (acc : A) (x : C), f acc (h x) = g acc x
  ============================
   (fold_left f (map h l') acc = fold_left g l' acc)


DEBUG:Going to execute:
induction l' in acc |- *; cbn
DEBUG LTAC Evaluated term: (hfg acc a)
DEBUG LTAC Evaluated term: (hfg acc a)
DEBUG LTAC Evaluated term: IHx