邱奇数

church encoding

0 ≡ λf.λx. x

1 ≡ λf.λx. f x

2 ≡ λf.λx. f (f x)

3 ≡ λf.λx. f (f (f x))

...

n ≡ λf.λx. fn x

...

plus(m,n)=m+n

f^{{(m+n)}}(x)=f^{m}(f^{n}(x))

…

只用lambda演算就构造了整个数学世界，太优雅了！

Using only lambda calculus to construct the entire mathematical world is too elegant!