 Combinatorial completeness guarantees that the term on the right hand side of the defining equation for \(+\) (i.e., the term \(Zmn(\textsf{V}(\textsf{KI}) (+(Pm)n)))\) can be transformed into a term in which \(+\) is the first, \(m\) and \(n\) are the second and third arguments, respectively. Then \(+\) can be defined explicitly as the fixed point of the combinator