Up tack

The up tack or falsum (⊥, \bot in LaTeX, U+22A5 in Unicode[1]) is a constant symbol used to represent:

• The truth value 'false', or a logical constant denoting a proposition in logic that is always false (often called "falsum" or "absurdum").[2]
• 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

• Mixed radix decoding in the APL programming language

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

See also

• Alternative plus sign
• Contradiction
• List of mathematical symbols
• Tee (symbol) (⊤)
• Verum

Notes

1. "Mathematical Operators – Unicode" (PDF). Retrieved 2013-07-20.
2. "Comprehensive List of Logic Symbols". Math Vault. 2020-04-06. Retrieved 2020-08-14.