`:::Based on the evidence presented here, I have no objection to changing our official definition to allow {0}, provided there's a reasonably prominent notice that the other convention exists. At Boolean-valued model I have kept the 0≠1 convention, because allowing {0} in that context is disastrous (and repeating ``nontrivial complete Boolean algebra`` could get tiresome), but added a footnote about it; interested parties are invited to comment on the wording of the footnote.    `