Absurdum

"Up tack" is the Unicode name for a symbol that is also called "bottom", "falsum", "absurdum", or "absurdity", depending on context. It is used to represent:The truth value 'false', or a logical constant denoting a proposition in logic that is always false. The bottom element in wheel theory and lattice theory, which also represents absurdum when used for logical semantics The bottom type in type theory, which is the bottom element in the subtype relation. This may coincide with the empty type, which represents absurdum under the Curry–Howard correspondence The "undefined value" in quantum physics interpretations that reject counterfactual definiteness, as in (r0,⊥)