 If the constants are \(\textsf{S}\) and \(\textsf{K}\), then the combinators are all those terms that are formed from \(\textsf{S}\) and \(\textsf{K}\) (without variables). Once we have defined \(\textsf{B}\) as \(\textsf{S}(\textsf{KS})\textsf{K}\), we may use \(\textsf{B}\) in further definitions as an abbreviation, and we do that primarily to reduce the size of the resulting terms as well as to preserve the transparency of the definitions.