\usepackage{../style}

\item {\bf (Optional)} If you want to run the code presented

      in the lectures, install the Scala programming language

      available (for free) from

      If you want to follow the code I present during the

      lectures, read the handout about Scala.

\item {\bf (Optional)} Have a look at the crawler programs.

      Can you find a usage for them in your daily programming

      life? Can you improve them? (For example in cases there

      are links that appear on different recursion levels, the

      crawlers visit such web-pages several times. Can this be

      avoided?) 

\item Read the handout of the first lecture and the handout

      about notation. Make sure you understand the concepts of

      strings and languages. 

\item In the context of the AFL-course, what is meant by the

      term \emph{language}?

\item Give the definition for regular expressions. What is the

      meaning of a regular expression?

\item Assume the concatenation operation of two strings is

      written as $s_1 @ s_2$. Define the operation of

      \emph{concatenating} two sets of strings.

\item Assume a set $A$ contains 4 strings and a set $B$ 7

      strings, how many strings are in $A @ B$?

\item How is the power of a language defined? (Hint: There are

      two rules, one for $\_^0$ and one for

      $\_^{n+1}$.)

\item How many regular expressions are there to match the

      string $abc$? (How many if they cannot include

      $\epsilon$ and $\varnothing$? How many if they also are

      not allowed to contain stars? How many if they also are

      not allowed to contain $\_ + \_$?)

\item When are two regular expressions equivalent? Can you

      think of instances where two regular expressions are

      equivalent, but it is not so obvious that they are? For

      example $a + b$ and $b + a$ do not count\ldots they

      are obviously equivalent.