 Given any system such as integer arithmetic or real arithmetic, we can write \(T\) for the set of all definite terms such as \(1 + (2/3)\) built from constants and constituting the definite language, and \(T[V]\) for the larger indefinite language permitting variables drawn from a set \(V\) in place of some of the constant symbols, with terms such as \(x + (2/y)\). When \(V\) contains only a single variable \(“x”\), \(T[\{“x”\}]\) is usually abbreviated to \(T[“x”]\) or just \(T[x\)] which is usually unambiguous. This convention extends to the algebra \(\Phi\) of terms of \(T\) together with its list of operation symbols viewed as operations for combining terms; we write \(\Phi[V\)] and call it the term algebra on \(V\). 