this post was submitted on 11 Feb 2024
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Ok, at some point we made a big mistake. (lemmy.world)
submitted 9 months ago* (last edited 9 months ago) by [email protected] to c/[email protected]
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Hacker News post about this: https://news.ycombinator.com/item?id=39309783 (source available)

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[–] [email protected] 44 points 9 months ago

TL;DR: Grid<A,B,C,D,E,F,G,H> simplifies to true, if and only if it is a 3x3 magic square.

full explanation

  • Fifteen is an array of length 15
  • T<A,B,C> checks if an array of length A+B+C is equivalent to an array of length 15, thus checking if A+B+C is equal to 15
  • And<A,X> is simplifies to X if A is true, else it simplifies to false
  • Df<A,B,X> checks if A and B are Diffrent , simplifying to X if they are
  • Grid<A,B,C,D,E,F,G,H> first checks if every row, column and diagonal is equal to 15, then checks if every item is unique.