The hyperlink of the first reference is invalid:
1. [Lambda Calculus](https://en.wikipedia.org/wiki/Lambd.a_calculus). Wikipedia: The Free Encyclopedia
it should be
1. [Lambda Calculus](https://en.wikipedia.org/wiki/Lambda_calculus). Wikipedia: The Free Encyclopedia

Good job, thank you!

one notice: when I try to use it to check something like tail for church list, I have to type rather many symbols. and it is a bit annoying to fix mistypes and check parts of expressions.

if it would be possible to have something like

let NIL = \c n. n
let CONS = \e l c n . e c (l c n)

this would be very helpful.
what do you think?

In the Simply Typed Lambda Calculus section, under Examples, In one instance it says λrarr instead of λ→