2  How to Design Programs

2.1  Programs are Function Definitions and Variable Definitions

2.2  Errors

2.3  The Recipe

3  Conditional Expressions and Functions

3.1  Drawing a UFO, Again

3.2  Landing the UFO

3.3  Hitting the UFO with a Shot

3.4  Booleans, Relations, and Conditions

3.5  Functions that Test Conditions

3.6  Designing Conditional Functions

4  Symbolic Information

4.1  Controlling the Anti-UFO Vehicle

4.2  Symbols, Characters, and Strings

4.3  Pictures and Images

5  Compound Data, Part 1: Structures

5.1  Shooting Down UFOs: The First Complete Game