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An upside-down T standing for a contradiction.
Also known as: Contradiction sign, Absurdity sign, Bottom element
Falsum is the proposition that is false under every interpretation. Deriving it is how a proof by contradiction ends, and the same character means 'perpendicular' in geometry and 'undefined' in some computing texts.
Denotes the constantly false proposition, from which anything follows and whose derivation completes a proof by contradiction.
Contexts: Mathematics
Shares its character with the perpendicular sign of geometry and with the bottom element of an ordered set, so its reading depends on the branch.
Contexts: Mathematics
A horizontal line with a shorter upright stroke rising from its centre, forming a letter T stood on its head.
The same character carries a geometric meaning in another branch.