Chapter 12 completes the discussion of natural deduction with the presentation of the rules for identity, discusses the size of infinite sets and shows how to write a paper that combines counterargument with rebuttal.

Formal topics:

• Identity
• Cardinality

Informal topics:

• Combining counterargument with rebuttal.

Supplementary topics:

• The Continuum Hypothesis
• Sorites
• A spelling test
• Puzzles