What is the effect of conditioning divorce upon an impossible condition, specifically relating to the intention behind the phrase "one period"?

Primary text

If the intent was that one period from each wife should occur, this constitutes conditioning divorce upon the impossible. In this case, it is probable that the specification of "one period" is void, leaving the condition as merely "if you both menstruate." Alternatively, divorce does not occur because the specified condition (one period from each) is never met. A third possibility is that the divorce occurs immediately, voiding the condition, based on principles established for conditioning divorce upon the impossible.