The world of mathematics is full of unreachable corners, where unsolvable problems live. Now, yet another has been exposed. In 1900, the eminent mathematician David Hilbert announced a list of 23 key problems to guide the next century of mathematical research. His problems not only provided a road map for the field but reflected a more ambitious vision — to build a firm foundation from which all mathematical truths could be derived. A key part of this vision was that mathematics should be “compl...