[texhax] where are latex functions defined?

[William F. Adams]

> Joe Cornelli said:
>> Thank you - that was helpful.  Now for a follow up question,
>> where are the TeX functions defined?

and Robin replied:
> in the texbook or tex the program or ...
>
> http://www.tex.ac.uk/cgi-bin/texfaq2html?label=books+tutorials

There's also a file somewhere, which interweaves plain.tex w/ the 
matching material from _The TeXbook_ so as to turn plain.tex into a 
literate program (wonder how DEK forgot to do that ;), which while it 
kind of skirts the matter of the license for _The TeXbook_ source, _is_ 
kind of interesting to read.

William
(who has said file at home, but can't recall where he found it)