Question 1: build Regular Expressions for the following :

1. Accepts only those words that begin or end with a double letter.
2. Accept only those words that have exactly four letters
3. accept only those words that have fewer than four letters.
4. Accept only those words that have at least four letters
5. Accept the language of all words with only a's or only b's in them.
6. Accepts language of all words having even number as and odd number of bs.
7. Build a RE that accepts language of all words having odd number as and odd number of bs.
8. Build a RE that accepts language of all words having number of as multiple of two each word while number bs can be arbitrary.
9. Build a RE that accepts language of all words having even number as and odd number of bs.
10. Accepts language of all words that if start with a then length must be odd and if starts with b then number of bs must be odd.