[sfvisser]

This one feels more apt to me: the derivation of a single lambda calculus term in which you can express all other expressions.

> The systematic construction of a one-combinator basis

https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&d...

[tromp]

It's not the shortest lambda term with that property though. That's λx λy λz. x z (y (λ_.z)) [1]

[1] https://en.wikipedia.org/wiki/SKI_combinator_calculus