– Prove that the set of even natural numbers is countably infinite.

2.1: ( \emptyset, 1, 2, 3, 1,2, 1,3, 2,3, 1,2,3 ) → ( 2^3 = 8 ) subsets. 2.2: (a) T, (b) F (empty set has no elements), (c) T, (d) T. Chapter 3: Set Operations Focus: Union, intersection, complement, difference, symmetric difference.

5.1: ( A \times B = (a,1),(a,2),(a,3),(b,1),(b,2),(b,3) ); ( B \times A ) has 6 pairs reversed. 5.2: ( |A \times B| = m \cdot n ), so ( |\mathcalP(A \times B)| = 2^mn ). Chapter 6: Functions and Relations Focus: Function as a set of ordered pairs, domain, codomain, image, preimage.

He handed each student a scroll. On it were exercises that grew from simple membership tests to the paradoxes that lurked at the foundations of mathematics. “Solve these,” he said, “and the keys shall be yours.”

– Prove ( (A \cup B)^c = A^c \cap B^c ) using element arguments.

– Show that ( \mathbbR ) is uncountable (sketch Cantor’s diagonal argument).