Plus sign in triangle usage (or minus, times)

[scop]

Can anyone refer me to a paper where the "plus sign in triangle", "minus sign in triangle", and/or "multiplication sign in triangle" are used? I'm reading a paper from the 80's where these symbols act on an image ("internal law" and "external law"); however, I'd like to see the symbols applied elsewhere. A textbook resource is fine as well. Thank you!
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[SteamKing]

Can anyone refer me to a paper where the "plus sign in triangle", "minus sign in triangle", and/or "multiplication sign in triangle" are used? I'm reading a paper from the 80's where these symbols act on an image ("internal law" and "external law"); however, I'd like to see the symbols applied elsewhere. A textbook resource is fine as well. Thank you!
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It's difficult to decipher what these symbols mean. Can you provide a reference or a link to the paper in which you found them? Sometimes, authors create special symbols to express concepts which have otherwise not been explored.