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README.md

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+2015 edition
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+
 Racket solutions & explanations for the [Advent of Code](http://adventofcode.com) puzzles. Written in Racket's literate-programming dialect, `scribble/lp2`.
 
 Install from the command line:
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 Explanations will be installed automatically as part of the Scribble documentation.
 
 [Or just read the code and explanations online, right now.](http://pkg-build.racket-lang.org/doc/aoc-racket/)
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+2016 edition
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+Solutions (implemented as `#lang` DSLs) in [`2016` directory](https://github.com/mbutterick/aoc-racket/tree/master/2016) (no explanations)
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+2017 edition
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+Solutions (implemented as `#lang` DSLs) in [`2017` directory](https://github.com/mbutterick/aoc-racket/tree/master/2017) (no explanations)