Chapter 1: Stacks
Chapter 2: Reverse Polish Notation
Chapter 3: Australia
Chapter 4: Penal transportation
Chapter 5: Slavery
Chapter 6: Prostitution
Chapter 7: Pornography
(and I wasn't even trying)
Computer science
Internet
Pornography
Bam!
Regardless, the assumption that pornography would be in every book assumes that you don't cluster the data to topics with strong clique behavior and normalize the data to remove overly-linked (aka obvious) topics.
