p 85 # 15, 16

p 95 # 12, 22, 26, 40a, 41a, 47.

Remark: The idea behind #47 has been advanced as a definition 

of the positive integers. 

p 109 # 2, 6ab, 7d, 8fgh, 10, 11, 16, 18, 26, 27, 31, 32, 33, 49, 48, 65.


p 142 # 3, 7, 12, 19, 21, 32, 51, 55.