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It is not a compiler error (2017)
From the highly eclectic blog of Mark Dominus
I have a file of (obnoxious) Good Advice for Programmers that I wrote about twenty years ago, and one of these items is: As I mentioned a few months ago, I built a simple phone app that Toph and I can use to find solutions to “twenty-four puzzles”. These would be indexed under the key 1455, which is the same puzzle, because each list of solutions is associated with the four input numbers in ascending order.
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