Consider the following relational schema:

Student (sid, sname, address)

Course (cid, cname, subject)

Enrolled (sid, cid)

Where subject can be Math, English, CS, Physics, etc. Now, write the Relational Algebra (RA), Tuple Relational Calculus (TRC), and Domain Relational Calculus (DRC) to answer each of the following queries. Note that some of these queries might not be expressible in Relational Algebra or Relational Calculus. For such queries, informally explain why they cannot be expressed:

a. Find the names of students who are enrolled in some Math or CS courses.

b. Find the sid(s) of the student(s) who enrolled in all the CS classes.