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9 \HEADER |
9 \HEADER |
10 |
10 |
11 \begin{enumerate} |
11 \begin{enumerate} |
12 |
12 |
13 \item If a regular expression $r$ does not contain any occurrence of $\ZERO$, |
13 \item If a regular expression $r$ does not contain any occurrence of $\ZERO$, |
14 is it possible for $L(r)$ to be empty? |
14 is it possible for $L(r)$ to be empty? Explain why, or give a proof. |
15 |
15 |
16 \item Define the tokens and regular expressions for a language |
16 \item Define the tokens and regular expressions for a language |
17 consisting of numbers, left-parenthesis $($, right-parenthesis $)$, |
17 consisting of numbers, left-parenthesis $($, right-parenthesis $)$, |
18 identifiers and the operations $+$, $-$ and $*$. Can the following |
18 identifiers and the operations $+$, $-$ and $*$. Can the following |
19 strings in this language be lexed? |
19 strings in this language be lexed? |