In ordinary arithmetic there are two special numbers, I and 0, with the properties that n *

Question:

In ordinary arithmetic there are two special numbers, I and 0, with the properties that n * 1 = 1 * n = n
And n * 0 = 0 * n = 0 for all number n. What relations (if any) play analogous roles in the relational algebra? Investigate the effect of the algebraic operations discussed in this chapter on those relations.