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- A logical constant denoting a false proposition in logic, often called "falsum" or "absurdum"
- The bottom element in lattice theory, which also represents absurdum when used for logical semantics
- The bottom type in type theory, which also represents absurdum under the Curry–Howard correspondence
as well as
The 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.
The similar-looking perpendicular symbol (⟂,
\perp in LaTeX, U+27C2 in Unicode) is a binary relation symbol used to represent:
- Perpendicularity of lines in geometry
- Orthogonality in linear algebra
- Independence of random variables in probability theory
- Comparability in order theory
- Coprimality in number theory
- "Mathematical Operators – Unicode" (PDF). Retrieved 2013-07-20.