[lisper]

It was an attempt to find the simplest possible mathematical system that was universal, i.e. could compute any function. It turns out that the answer is that function application by itself is universal (if functions are first-class entities). This was a surprise at the time, and it still generally surprises people today when they first learn of it.

You might find this interesting:

https://flownet.com/ron/lambda-calculus.html