Answer to Question #38225 in Math for Sujata Roy

Question

Explain the following statements and determine whether they are true or false.

1) Complement of a CFL need not be recursive
2) If L is recursive then (L)^+ is also recursive.
3) If L1 is recursive and L2 is recursively enumerable then L2 - L1 is need not be recursively enumerable.
4)Recursive sets are closed under complement and substitution.