In some languages, a logical symbol (or a $0$-ary connective) used as a constant to denote a formula. One propositional constant that is frequently encountered in intuitionistic logic is falsum ($\perp$), intended as a representation of a generic contradiction or falsehood; intuitionistic negation is often defined as $\phi \to \perp$. Other examples include constants t and f that feature in many studies of relevant logic and some enrichments of fuzzy logics including a constant for each truth value in the interval $\left[0,1\right]$.