 The combinatory base \(\{\textsf{B},\textsf{C},\textsf{W},\textsf{I}\}\) is especially interesting, because these combinators suffice for a definition of a bracket abstraction that is equivalent to the \(\lambda\)-abstraction of the \(\lambda\textsf{I}\)-calculus.  To put it differently, all functions that depend on all of their arguments can be defined by this base. The other base allows the definition of functions that can be described by terms in the class of the so-called hereditary right maximal terms (cf. Bimbó 2005). Informally, the idea behind these terms is that functions can be enumerated, and then their successive applications should form a sequence in which the indexes are “globally increasing.”