python07():
  Exercises for making choices.

  Bus fare example:

  Age 65  pays  2.5
  Age 3  pays  0.0
  Age 9  pays  1.35

  Collatz example.

1 37
2 112
3 56
4 28
5 14
6 7
7 22
8 11
9 34
10 17
11 52
12 26
13 13
14 40
15 20
16 10
17 5
18 16
19 8
20 4
21 2
22 1
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 1

  Greatest common divisor using while(True)

seeking greatest common divisor of 34578 and 6215
34578 6215 3503
6215 3503 2712
3503 2712 791
2712 791 339
791 339 113
339 113 0
gcd is 113

  Bicycle combination example.

  Yesterday:  4 0 4  Today:  4 0 5
  Yesterday:  5 1 7  Today:  5 2 0
  Yesterday:  6 7 7  Today:  7 0 0
  Yesterday:  7 7 7  Today:  0 0 0