“I am shopping for a linear model,” you ask. And indeed you are shopping for equations and statistical models. The shop is dark and over-crowded with esoteric artifacts. In the center of the room, the hideously androgynous shopkeeper (wispy tufts of white hair, green skin, a crooked nose, and pinhole eyes hiding behind thick glasses) stirs an huge black cauldron. Smoke bubbles over the side of the cauldron and makes Greek letters on the floor. Sigma, beta, theta, phi… You haggle over the price of a Poisson distribution and the shopkeeper agrees to sell you a suitable equation for two gold pieces and your first p less than point-oh-five.