Lulu's guidelines seem to cover all bases. The sort of thing a lawyer would churn out. But even in all of those words it does not precisely say what it refers to. There's just this >> 'Illegal Items- Content sold through the Lulu Site must adhere to all applicable laws.' So it's really up to the writer to look them up. If in doubt then that Adult option is a good idea. It does not actually stop anyone under 18 (or whatever) from buying a book or even reading a Preview of it.