$5)$Consider the following schema:

Sailors $($sid$,$ sname, rating, age$)$

Boats $($bid$,$ bname, color$)$

Reserves $($sid$,$ bid, day$($date$))$

Write relational algebra expression for the following queries.

a$)$Find the ids and names of sailors who have reserved two different boats on the same day.

b$)$Find the names of all sailors who have reserved a boat but have not reserved a red boat.