... that only four proofs are required (A ⇒ B, B ⇒ C, C ⇒ D, and D ⇒ A) as opposed to the six proofs (A ⇒ B, B ⇒ A, A ⇒ C, C ⇒ A, A ⇒ D, and D ⇒ A) required to show that A is equivalent to each of the ... which it must be shown that B3 : x ≤ t To so, work forward from A2 and the definition of the set S in the hypothesis to obtain A3 : x(x − 3) ≤ From A3, either x ≥ and x − ≤ 0, or, x ≤ and x − ≥ But ... which a|b and b|c A1 : b = pa and c = qb, where p and q are both integers 3.7 (T = true, F = false) a Truth Table for “A AND B.” A B “A AND B” T T F F T F T F T F F F WEB SOLUTIONS TO EXERCISES...