Create regular expressions for the following:

1. L(r)= {w {a,b}* : w contains at least two a's }

2. L(r)= {w {a,b}* : w begins and ends with the same symbol }

3. L(r)= { aⁿb^m : n+m is even }

4. L(r)= {w {a,b}* : 3rd symbol of w from the right is a }