Goal:
  
  A : Type
  size : A → nat
  a : A
  l : list A
  IHl : list_size (rev l) = list_size l
  ============================
   (list_size l + list_size [a] = S (size a + list_size l))


DEBUG:Going to execute:
cbn
DEBUG LTAC Evaluated term: rev_cons
DEBUG LTAC Evaluated term: rev_cons
DEBUG LTAC Evaluated term: list_size_app
DEBUG LTAC Evaluated term: list_size_app
DEBUG LTAC Evaluated term: IHl
DEBUG LTAC Evaluated term: IHl