Algorithms (Sec 3.1, Appendix 3): Def 1 of algorithm (p191), Properties of algorithms (p193).
Number systems (Sec 4.1, 4.2): Def 1 of divides (p238), Theorem 2: the division algorithm (p239), Def 2 of div and mod (p239), Thm 1: base b expansion of n (p246), Algorithm 1: constructing base b expansion (p249)
Predicates and quantifiers (Sec 1.4, 1.5): Sec 1.4: Definition of predicates on p. 37 and Example 1, Definition 1, Definition 2, Table 1 and Table 2. Sec 1.5: Example 4 on page 59, Table 1, Example 14 on page 63.
Sets and Summations (Sec 2.1, 2.2, 2.4): Definition 1 of 2.1 (p. 116), the empty set (p. 118), Definition 3 (p. 119), Definition 6 (p. 121), Definition 8 (p. 123). Definitions 1 through 5 of Section 2.2 (pp. 127-129). Generalized union in Definitions 6 and 7 of p. 133. Summation notation on pp. 162-163
Induction (Sec 5.1): Principle of Mathematical Induction (p. 313), Example 1 (p. 316), Example 3 (p. 318)