Let the following relation schemas be given:

R = (A, B,C)

S = (D, E, F)

Let relations r(R) and s(S) be given. Give an expression in the tuple relational

calculus that is equivalent to each of the following:

a. $\prod _A(r)$

b. $\sigma _{B =17} (r )$

c. r × s

d. $\prod _{A,F} (\sigma _{C = D}(r × s))$