I happened upon the [church-encoding](https://stackoverflow.com/questions/tagged/church-encoding "show questions tagged 'church-encoding'") tag which features a link to a supposedly free book. 

> 
> [An Introduction To Functional Programming Through Lambda Calculus](http://cs.fit.edu/~ryan/library/functional_programming/gjm.lambook88.pdf) by Greg Michaelson
> 
> 
> 

However, the link leads to a 403 Forbidden page for that resource.

I tried googling the book to see if I could find a substitute link but I couldn't find a free version of the book. I admit, I didn't look too hard but I am also not familiar with the subject matter or which sources would be good. In addition, since I failed finding a free version even after brief searching, I wonder if the book is still free - perhaps that's not the case any more. That is something that I'm again not sure how to verify.

I hope somebody who is more familiar with the situation would be able to either provide a working link to a free copy or, if the book is not free, then the link can be taken down.