Combinators

• Combinator Birds: Index of combinators with SKI equivalents

  https://www.angelfire.com/tx4/cus/combinator/birds.html

Combinators are lambda abstractions without free variables, that is, closed lambda terms.

The identity function returns whatever argument it is applied to: $\quad\ \lambda x.x$

Self application function applies its argument to its argument: $\quad\ \lambda f.ff$