sdiehl

TRUE = lambda x: lambda y: x
FALSE = lambda x: lambda y: y
Product = lambda x: lambda y: lambda z: (z)(x)(y)
And = lambda x: lambda y: (x)(y)(x)
Not = lambda x: lambda y: lambda z: (x)(z)(y)
Boolean = (Product)(True)(False)
Succ = lambda x: lambda y: lambda z: (y)((x)(y)(z))
Pred = lambda x: lambda y: lambda z: x(lambda i: lambda j: j(i(y))) (lambda k: z) (lambda k: k)
Y = lambda g: (lambda z:z(z)) (lambda f: g(lambda arg: f(f)(arg)))
Nth = Y(lambda f: lambda n: Succ(f(n-1)) if n else Zero)

cdepillabout

let
  nixpkgs-src = builtins.fetchTarball {
    # master of 2021-01-05.
    url = "https://github.com/NixOS/nixpkgs/archive/1a57d96edd156958b12782e8c8b6a374142a7248.tar.gz";
    sha256 = "1qdh457apmw2yxbpi1biwl5x5ygaw158ppff4al8rx7gncgl10rd";
  };

  pkgs = import nixpkgs-src {
    config = {
      # allowUnfree may be necessary for some packages, but in general you should not need it.