Iota and Jot (nonfiction)
In formal language theory and computer science, Iota and Jot (from Greek iota ι, Hebrew yodh י, the smallest letters in those two alphabets) are languages, extremely minimalist formal systems, designed to be even simpler than other more popular alternatives, such as the lambda calculus and SKI combinator calculus. Thus, they can also be considered minimalist computer programming languages, or Turing tarpits, esoteric programming languages designed to be as small as possible but still Turing-complete. Both systems use only two symbols and involve only two operations. Both were created by professor of linguistics Chris Barker in 2001. Zot (2002) is a successor to Iota that supports input and output.
Universal iota combinator
Question: How can the iota combinator be universal if its definition includes S and K?
Answer by Mark Gritter:
The reason we say Iota is universal is because any (computable) function can be expressed in terms of just ι. No S or K are necessary to write a function in Iota.
Iota’s denotational semantics are defined in terms of auxiliary programs S and K, but the language itself has only the symbol ι (and parentheses, or some other tree structure such as the star notation given here: Iota - Esolang) So to interpret what an Iota expression means, you might have to use S and K, but then you’ve crossed into being an interpreter, not a programmer.
https://www.quora.com/How-can-the-iota-combinator-be-universal-if-its-definition-includes-S-and-K