What is considered good style for writing small numbers as words or digits in mathematical texts?
I have three concrete examples, are there any differences between those?
- "M is a matroid of rank six" vs. "M is a matroid of rank 6"
- "There are six elements in the set" vs. "There are 6 elements in the set"
- "The numbers a and b differ by one" vs. "The numbers a and b differ by 1".
Are there any general rules?
Edit: Not to influence your answers, but I'm asking the question because a copy-editor of the London Math. Society changed all the above to use the digits while we had words in our manuscript. I'm not a native speaker, but I usually use words for small digits.