Construct a regular expression that defines the language L a$)$ Give a possible regular expression that generates the language L consisting of all words in which

all words

$$ either contain no a$$s at all, or

$$ when there are a$$s$,$ they occur in clumps of three or more a$$s$,$ and

$$ when there are a$$s$,$ there are an even number of such clumps of a$$s$.$

For instance, words such as b$,$ bbbbbaaaabaaaaabbb and aaabbbaaaaaabaaabaaab are words

in this language, and words such as aaaa and aaabaa are not words in the language.

b$)$ Construct a regular expression that defines the language L containing all words with at least one

aab$-$substring or all words with at least one ba$-$substring.