More than 200 economists, tech bosses and researchers from across the globe have put their names on a short, sharply worded open letter cautioning that artificial intelligence is on track to shake up the job market in a big way, and that governments are lagging behind. Organised by the Stanford Digital Economy Lab, the letter is titled "We Must Act Now," with the subtitle "A Statement on AI's Transformation of the Economy." It runs to just 88 words, and every one of them appears to have been chosen with care.