The criteria for special margins are: must be displayed, signs of comparison are vertically aligned in print, and no sign of comparison may be preceded by any expression on its left. If your expression satisfies these requirements then you would use special margins. It's easier to answer something like this when I can see a picture of the actual print. I am assuming that your expression is not embedded and that the equal signs all line up vertically. If that is the case, the word "or" should have no impact on your formatting.