In 1968, ecologist Garrett Hardin popularised a grim idea: a shared pasture always ends up overgrazed, since everyone gains by adding one more cow. Elinor Ostrom studied fisheries, forests and irrigation systems that had been managed in common for centuries. With local rules and mutual monitoring, it works. In 2009, she became the first woman to win the Nobel Prize in economics.
How many different structures can you build with six classic 2-by-4 Lego bricks of the same colour? The company used to quote just over 102 million. In 2005, Danish mathematician Søren Eilers recounted everything by computer: 915,103,765 combinations. The official estimate had been too low by a factor of about nine.
Fold an A4 sheet in half and you get an A5 with the same proportions. That only works for one ratio between length and width: about 1.414, the square root of 2. The A0 format measures exactly one square metre, and A4 is a sixteenth of it. With standard 80-gram-per-square-metre paper, an A4 sheet therefore weighs exactly 5 grams.