derivative of cat|dog and c is der(cat,c) | der(dog,c), which is at|∅ and simplifies to at
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The way that most programs interact with the Unix terminal is through ANSI escape codes. These are special codes that your program can print in order to give the terminal instructions. Various terminals support different subsets of these codes, and it's difficult to find a "authoritative" list of what every code does. Wikipedia has a reasonable listing of them, as do many other sites.