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Logic matrix

These diagrams are equivalent representations of the 2-ary boolean functions. What are the symbols used in the top left diagram?

(Source: wikicommons user mate2code)

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    $\begingroup$ I'm fairly certain that the symbols in the upper left diagram are not standard in the field of symbolic logic. $\endgroup$ – Trevor Wilson Mar 21 '13 at 1:52
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    $\begingroup$ I'm not even going to follow your link, but I predict it's an illustration created by user "Lipedia". He (or she) is somewhat infamous for creating extremely confusing and unclear (though sometimes visually beautiful) "visualizations" of a range of discrete math topics. There's a good chance he invented some of this symbolism himself and nobody else uses it. $\endgroup$ – hmakholm left over Monica Mar 21 '13 at 1:55
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    $\begingroup$ It looks like Lipedia's account is now called Mate2code. I don't think he's a troll; he's way too prolific and lavishes too much loving care on his illustrations for that. But he also has a real problem with understanding which kind of diagrams will be any use for a reader. $\endgroup$ – hmakholm left over Monica Mar 21 '13 at 2:01
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    $\begingroup$ It appears to be what he calls Nibble Shorthands, which represent nibbles, I guess. You could probably ask him how he came up with them and why their shapes make sense, I would bet he has a beautiful answer. $\endgroup$ – Alfonso Fernandez Mar 21 '13 at 2:14
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    $\begingroup$ @AlfonsoFernandez: That's as close to an answer as we'll ever get, I think. (I tend to use the symbols 0123456789ABCDEF to represent nibbles, but I'm just a freak, I suppose). $\endgroup$ – hmakholm left over Monica Mar 21 '13 at 2:20
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Based on a comment by Henning Makholm and a short link trace I conducted, these are nonstandard symbols invented by Wikimedia user mate2code (formerly Lipedia).

mate2code calls them nibble shorthands, and they simply represent all possible nibbles (four digit binary strings, more commonly represented by the numbers $0$ to $15$ or by the hexadecimal digits 0 to F), in an order which can be seen here (by interpreting the red dots under each symbol as $1$'s and the white dots as $0$'s).

Note: The links may be volatile, as they refer to Wikimedia user pages.

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