2.3 Vertical Thinking
  2.3.1 Tennis Example
  2.3.1.1 Solution
  2.3.1.2 Comment
  2.3.2 Definition
  2.3.2.1 Highway Illustration
  2.3.2.2 Digging Holes
  2.3.3 Logic
  2.3.3.1 Experts
  2.3.3.2 Boundaries
2.3.4 Consequences
2.3.5 Criticisms