I am in the final stages of writing a book and currently I am preparing the index. Are there any rules whether index entries should be listed in singular or plural? Currently I have
Markov chains, 20, 30-40, 50
with discrete state space, 33
with continuous state space, 38
Should I change this to "Markov chain"?
I would say it depends on how the item is discussed in the body of the book.
If a Markov chain is something referred to as a single entity, then index it as a single item. If you discuss several of them at once, or generalize (like saying "black holes have thus-and-such properties"), I'd use the plural.
