Which of the following are decidable?
$$1.$$ Whether the intersection of two regular languages is infinite
$$2.$$ Whether a given context-free language is regular
$$3.$$ Whether two push-down automata accept the same language
$$4.$$ Whether a given grammar is context-free

Which of the following statements are true?
$$1.$$ Every left-recursive grammar can be converted to a right-recursive grammar and vice-versa
$$2.$$ All ε-productions can be removed from any context-free grammar by suitable transformations
$$3.$$ The language generated by a context-free grammar all of whose productions are of the form $$X \to w$$ or $$X \to wY$$ (where, $$w$$ is a string of terminals and $$Y$$ is a non terminal), is always regular
$$4.$$ The derivation trees of strings generated by a context-free grammar in Chomsky Normal Form are always binary trees

If $$L$$ and $$\overline L $$ are recursively enumerable then $$L$$ is

Which of the following is true for the language $$\left\{ {{a^p}} \right.\left| P \right.$$ prime $$\left. \, \right\}$$?