Hyphens, En Dashes, Em Dashes

Q. I’m wondering about the proper uses of the prefix auto-. When one cannot find the word using this prefix in the dictionary, is there a standard for how to use it? To hyphenate or not to hyphenate, that is the question. My specific example is autosequence, auto-sequence, or auto sequence. Which would Chicago recommend?

A. All prefixes form words that are closed unless the word it is joined with is a proper noun, or if there would be ambiguity owing to, for example, a doubled letter, or if the hyphenated version is in the dictionary:


auto-destruction [hyphenated, I would suppose, because it is analogous to self-destruction]


auto-ovulation [to avoid double o]