diff -r 13ff10d9717a -r 04264d0c43bb hws/hw03.tex --- a/hws/hw03.tex Mon Oct 07 09:34:12 2013 +0100 +++ b/hws/hw03.tex Mon Oct 07 09:45:11 2013 +0100 @@ -9,6 +9,8 @@ \section*{Homework 3} \begin{enumerate} +\item What is a regular language? + \item Assume you have an alphabet consisting of the letters $a$, $b$ and $c$ only. (a) Find a regular expression that recognises the two strings $ab$ and $ac$. (b) Find a regular expression that matches all strings \emph{except} these two strings. @@ -18,7 +20,7 @@ \end{center} \item Define the function $zeroable$ which takes a regular expression as argument -and returns a boolean.\footnote{In an earlier version there was an error.} The +and returns a boolean. The function should satisfy the following property: \begin{center} $zeroable(r)$ \;if and only if\; $L(r) = \varnothing$