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)
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
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