 Syntax: For any formula \(\phi\) and any finite sequence \(x_1 , \ldots ,x_n\) of variables, the expression ‘\(\lambda x_1 \ldots x_n [\phi]\)’ is a predicate symbol of arity n. Extend the notion of free and bound variables (using the functions \(\mathbf{FV}\) and \(\mathbf{BV})\) in such a way that