A truth function is a function that returns one of two values, one of which is interpreted as ``true,'' and the other which is interpreted as ``false''. Typically either ``T'' and ``F'' are used, or ``1'' and ``0'', respectively. Using the latter, we can write $$f : \{0,1\}^n \rightarrow \{0,1\}$$ defines a truth function $f$ That is, $f$ is a mapping from any number ($n$ of true/false (0 or 1) values to a single value, which is 0 or 1.