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?