Hope Reeves writes: Delta Air Lines will soon introduce planes that have on-board lavatories even smaller than the three-by-three-foot ones we currently enjoy. The littler loos on the airline’s new fleet of Boeing 737-900 planes will allow Delta to squeeze four more seats into economy class. (As if flying coach were not already luxurious enough.) “The redesigned lavs use the existing interior more efficiently while taking up less footprint space inside the aircraft,” said Anthony Black, an airline spokesman. After all, who doesn’t love an efficient bathroom?