 To demonstrate the sense in which definability is understood here we consider the example of \(\textsf{B}\). The axiom for \(\textsf{B}\) is \(\textsf{B} xyz\triangleright_1x(yz)\), and if we take \(\textsf{S}(\textsf{KS}) \textsf{K}\) instead of \(\textsf{B}\), then the following reduction sequence results.