Goal:
    A : Type  l : list A  l' : list A
  ============================
   (0 = 0)


DEBUG:Going to execute:
done
DEBUG LTAC Evaluated term: firstn_app
DEBUG LTAC Evaluated term: firstn_app
DEBUG LTAC Evaluated term: firstn_all
DEBUG LTAC Evaluated term: firstn_all
DEBUG LTAC Evaluated term: Nat.sub_diag
DEBUG LTAC Evaluated term: Nat.sub_diag
DEBUG LTAC Evaluated term: firstn_0
DEBUG LTAC Evaluated term: firstn_0
DEBUG LTAC Evaluated term: Prop
DEBUG LTAC Evaluated term: Prop