I asked a similar question in the old forum, but I can't find anything to back this up.
I run into many equations where there is a displayed expression followed by another equation (on the same line in print). The second equation establishes the conditions for the first equation (e.g., that x does not equal zero, or that xsub1 is greater than or equal to xsub2). Sometimes there is a comma following the first equation, sometimes there is just a lot of space, and sometimes the second equation is in parentheses. My inclination is to start the second equation on a new line. Is there a rule about this?
I consider this kind of thing to be an author's comment to the equation, in which case I usually place it following on the same line in braille with any runovers in the established runover position. I don't believe there is a rule specifically addressing this situation. If there could be confusion about the "meaning' of this additional material, and it is not differentiated in print with a comma or other punctuation, I have, on occasion, placed a note on the TN page stating that comments to equations or procedures are enclosed in brackets (or whatever) and follow on the same braille line.
I am wondering what the heirarchy is for dividing such a thing. Suppose that the first equation is long and needs to be divided one or more times. Wouldn't logic dictate that the "expression" should be divided also at the level of the second separate equation, since that is of a higher order even than a sign of comparison?