Let $L_1, L_2$ be two regular languages and $L_3$ a language which is not regular. Which of the following statements is/are always TRUE?

Consider the Deterministic Finite-state Automation (DFA) $$A$$ shown below. The DFA runs on the alphabet {0, 1}, and has the set of states {$$s,p,q,r$$}, with $$s$$ being the start state and $$p$$ being the only final state.

Which one of the following regular expressions correctly describes the language accepted by $$A$$?

Consider the following definition of a lexical token id for an identifier in a programming language, using extended regular expressions:

$$\mathrm{letter\to[A-Za-z]}$$

$$\mathrm{letter\to[0-9]}$$

$$\mathrm{id\to letter(letter\,|\,digit)^*}$$

Which one of the following Non-deterministic Finite-state Automata with $$\varepsilon $$-transmissions accepts the set of valid identifiers? (A double-circle denotes a final state)

Which of the following statements is/are CORRECT?