There is something steampunk about the extreme-ultraviolet lithography, or EUV, machine. To a layman’s eyes, this bus-sized box of pipes, wires and cylinders looks part Heath Robinson, part “Blake’s 7”. Even the wizardry inside seems to blend the industrial and information ages: it prints semiconductors by firing lasers at molten tin. Yet this is the only contraption that makes chips sophisticated enough to power the world’s leading artificial-intelligence models. And it is only produced by one company, ASML, which is Dutch.

So I was intrigued to learn that Howard Lutnick, America’s commerce secretary, had expressed fears that, despite strict export controls, one of these machines had got to China. After I spoke to ASML, which denies that allegation, my curiosity grew. Why would Mr Lutnick (who has not yet shared evidence with ASML) make such a claim? And what to make of recent reports that China has built its own EUV machine? If you want to understand the dispute over this prized technology, read the full story.