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Droste’s Lair
A swords-and-sorcery programming environment for building and counting mathematical structures
An evil sorceror is tormenting a nearby village with an insidious puzzle: How many ways, he asks, can a 2xN checkerboard be covered completely with dominoes? What we have here suggests a gentle loosening of this constraint to allow making multiple simultaneous tail-recursive calls that commute with each other because they operate on different parts of a structure.) (We maintain a conceptual color scheme throughout the interface of Droste's Lair: yellow for actions, purple for procedures & calls, and red for trouble.)
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