1. a) f(x) is undefined for x = 0
   b) f(x) is complex for x < 0
   c) multivalued

2. a) multivalued
   b) It is
   c) undefined at x = 2

3. a) Z >= 0, {0..9}
   b) 0.. -> 1..?
   c) All bit strings -> N
   d) All bit strings -> N
   e) (Z^+)^2 -> Z^+
   f) (Z^+)^2 -> Z^+

4. a) 1 b) 2 c) -1 d) 0 e) 2 f) 3 g) 0 h) 2
5. a) 1 b) 0 c) 0 d) -1 e) 3 f) -1 g) 2 h) 1

8. a) 6 b) 24 c) 120 d) 3_628_800

10. a)y b)n c)n
11. {a}

12. a) y b) n c) n d) n
13. a) y b) n) c) y) d) n

14. ynyy

15. a) everyone has a phone number (phone numbers should already be uniquie)
    b) None (student ids should already be unique)
	c) Every student gets a unique grade
	d) no two people come from the same town

16. a) the set of phone numbers
    b) the set of student ids
	c) 1..100
	d) all towns

17. ynnn
18. a) { 1 }
    b) { -1, 1, 5, 9, 15 }
	c) { 0, 1, 2 }
	d) { 0, 1, 2 }

19. f.g = x^2 + 4x + 5, g.f = x^2 + 3
20. f + g = x^2 + x + 3
    fg = x^3 + 2x^2 + x + 2

21. f^-1 doesn't exist, assuming f^-1(x) = +sqrt(x)
   a) { 1 }
   b) { x | 0 < x < 1 }
   c) { x | x > 2 }