Marc Andreessen, a former revolutionary software engineer and now venture capitalist at Andreessen Horowitz (aka a16z), said this in a recent interview: "At our leading edge companies, estimates are the leading edge programmers are like 20x more productive than they were a year ago. It's like the most dramatic increase in programmer productivity in like ever." He's not the only respectable voice claiming this. Silicon Valley veteran Naval Ravikant, Brian Chesky (founder of AirBNB), and many other credible folks have made similar claims recently. And this is ignoring the less-credible claims of people who run AI companies. So is this 20X thing real? Or even 10X, 5X, maybe 2X? I think it only makes sense to look at long-term productivity, over a time scale of a year or more. So "20X" means that an individual, or a team, gets 20 years of pre-AI work done in a single year. Because if the long-term increase falls short of that, it's not really 20X, is it?…