I honestly haven't an idea how to proof that eventhough I can understand the background, could someone help me?

  • $\begingroup$ Welcome to CS.SE! Can you tell us more about what attempts you've made? What context-free languages do you know that aren't DCFL? Where have you looked? Have you checked in standard textbooks? $\endgroup$
    – D.W.
    Commented Jan 4, 2017 at 0:11
  • $\begingroup$ L1 = {a n b mc m ∣ n, m ≥ 0}That's what I thought to do: L ∪ {0} ∈ DCFL und (L ∪ {0})∗∉ DCFL. $\endgroup$
    – user64134
    Commented Jan 4, 2017 at 0:38