What was the name of the soup called that made Milo hungry in Digitoplis?

At the beginning of chapter 15, Milo, Tock, and the Humbug have arrived in Digitopolis through the help of the Dodecahedron. They find themselves eating a most peculiar meal with the number miners and the Mathmagician. They tuck in, expecting their heaping bowlfuls of soup to fill them up, but despite numerous refills they end up hungrier than before and equally bewildered. The Dodecahedron informs them that they have been eating the specialty of the kingdom, Subtraction Stew, and goes on to explain the meal system of the citizens of Digitopolis. The story line of Digitopolis leads the reader to think that perhaps the author Norton Juster incorporated his own love of number-play into the story, creating an entertaining and thoughtful contrast to Dictionopolis and their love of words.