diff -r 70c307641d05 -r 1e4da6d2490c hws/hw01.tex --- a/hws/hw01.tex Mon Sep 22 13:42:14 2014 +0100 +++ b/hws/hw01.tex Fri Sep 26 14:06:55 2014 +0100 @@ -37,7 +37,8 @@ \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. + \emph{concatenating}, written $\_ \,@\, \_$ two sets of + strings. \item Assume a set $A$ contains 4 strings and a set $B$ 7 strings, how many strings are in $A @ B$? @@ -47,14 +48,14 @@ $\_^{n+1}$.) \item How many regular expressions are there to match the - string $abc$? (How many if they cannot include + string $abc$? How many if they cannot include $\epsilon$ and $\varnothing$? How many if they are also not allowed to contain stars? How many if they are also - not allowed to contain $\_ + \_$?) + not allowed to contain $\_ + \_$? \item When are two regular expressions equivalent? Can you think of instances where two regular expressions match - teh same strings, but it is not so obvious that they do? For + the same strings, but it is not so obvious that they do? For example $a + b$ and $b + a$ do not count\ldots they obviously match the same strings, namely $[a]$ and $[b]$.