But still he visited Jakow night after night, with ever growing urgency, as though convinced that fluency in mental calculation would make of him an engineer, and as though becoming an engineer would advance him through the ranks. He routinely subtracted a digit from nine when he should be doubling it. Or tried to carry a one, although the very idea was meaningless in the new System. Jakow tried to think of real-life calculations that might make the System more concrete and learnable, but his word problems always felt contrived--purchases of military supplies, hours of sentry duty in a year--and could have no real application in Stefan's life. It was partly that Jakow had little knowledge of Stefan's life, but partly, too, that although Jakow understood the potential utility of his System, the joy he took in it had nothing to do with its practicality. For Jakow it was pure thought, abstract and aesthetic, the one realm where perfection was not only possible but required. He loved only the way its pieces snapped together in his brain. How they interlocked with the world was less clear to him.