[jdpage]

Aside from the zero/one thing, if I'm understanding this right, Nock is based on the SKI combinator calculus, where the combinators are

S: λxyz.xz(yz)

K: λxy.x

I: λx.x

From there, you can express anything from the lambda calculus, and vice-versa. So I think it's reasonable to say that Nock is just a machine-friendly way of expressing the lambda calculus.

[urbit]

I wouldn't say it's based on SKI - just relatively similar. There are a lot of ways to skin this cat.

SKI is obviously a lot simpler mathematically, but I wouldn't want to try to use it as a compiler target...

[jacquesm]

The 'I' is optional, all you need is S and K. I = (SKK)

You can go simpler still: Iota.