1. (8 points) Let L be a regular language. Define L' = {xay ? ?* | xy ? L, a ? ?}. We
take the strings in L, and add exactly one symbol anywhere in the string for anywhere
it could be placed, even possibly at the beginning or end. Prove that if L is regular,
then so is L'.
2. (8 points) Prove that \{0$^m$1$^n$ | $m \ge n$\} is not regular.
3. (8 points) Give a CFG for valid regular expressions over the alphabet ? = {a,b}. The
alphabet of your grammar should be over {a, b, (, ), U, *, ?, ?}. You may insert more
parenthesis than necessary. Here we shall use ? to represent the base-case regular
expression symbolizing the set only containing the empty string, that is, ? = {?}. Use
the symbol ? not as part of the regular expression, but if necessary, as part of the
right-hand-side of productions of the grammar to satisfy (V??)*. You must generate
all syntactically valid regular expressions.