Added 1.20

chapter1.tex

@@ -89,6 +89,19 @@ \section{Chapter 1}
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 \textbf{Solution:} \alreadyanswered
 
+%		1.20		%
+\item[1.20]For each of the following languages, give two strings that are members and two strings that are not members--a total of four strings for each part. Assume the alphabet $\Sigma = \{a,b\}$ in all parts.
+\begin{enumerate}
+\item[a.]\textbf{Solution:} 2 members: $ab, aa$; 2 not members: $ba, bab$.
+\item[b.]\textbf{Solution:} 2 members: $ab, abab$; 2 not members: $b, ba$.
+\item[c.]\textbf{Solution:} 2 members: $aa, bb$; 2 not members: $ba, ab$.
+\item[d.]\textbf{Solution:} 2 members: $\epsilon, aaa$; 2 not members: $b, bb$.
+\item[e.]\textbf{Solution:} 2 members: $aba, aaba$; 2 not members: $b, bb$.
+\item[f.]\textbf{Solution:} 2 members: $aba, bab$; 2 not members: $a, b$.
+\item[g.]\textbf{Solution:} 2 members: $b, ab$; 2 not members: $ba, bb$.
+\item[h.]\textbf{Solution:} 2 members: $a, ba$; 2 not members: $ab, b$.
+\end{enumerate}
+
 %		1.23		%
 \item[1.23]Let $B$ be any language over the alphabet $\Sigma$. Prove that $B = B^+$ iff $BB \subseteq B$.
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