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⊥ gets a lot of use, it can be the NOR operator, or the bottom element in a lattice, or just "false". https://en.wikipedia.org/wiki/Up_tack claims that there is a separate Unicode symbol for perpendicular, but it's not one by browser renders. :)

What is the source of this picture?

Up tack
The up tack or falsum (⊥, \bot in LaTeX, U+22A5 in Unicode) is a constant symbol used to represent:

The bottom element in lattice theory
The bottom type in type theory
A logical constant denoting "false" in logicThe glyph of the up tack appears as an upside-down tee symbol, and as such is sometimes called eet (the word "tee" in reverse). Tee plays a complementary or dual role in many of these theories.

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