Q6. (2 points) Section 4.1 Question 21: The tail of a language is defined as the set of all suffixes of its strings, that is, tail (L) = {y xy = L for some x = *}. Show that if L is regular, so is tail (L). Q7. (3 points) Section 4.1 Question 28: If L is a regular language, prove that the language {uv : u L, v = LR} is also regular. Section 4.3 Identifying Nonregular Languages Q8. (.5 point) Section 4.3 Question 1: **Show that the language is not regular. L= {a"be":n0, k 0} Q9. (3 points) Section 4.3 Question 17: Prove or disprove the following statement: If L1 and L2 are nonregular languages, then L UL2 is also nonregular.