A researcher plugged in 26,000 opinions issued by the Supreme Court between the early 19th century and the present day into his computer. “He treated each of these cases as a node and each citation from one case to another as a link. The result was a complicated web resembling a map of cities linked by dozens of airlines. He found the most important opinions, at least judged by how many times they were cited, by working out which nodes were likeliest to fall on the shortest paths between two other nodes. Intriguingly, the cases mostly come from an advanced and esoteric subject…