Def unzip(as) == <map(p.1of(p);as),map(p.2of(p);as)>

is mentioned by

Thm* as:(T1T2) List. zip(1of(unzip(as));2of(unzip(as))) = as	[zip_unzip]
Thm* as:T1 List, bs:T2 List. ||as|| = ||bs||    unzip(zip(as;bs)) = <as,bs>	[unzip_zip]

Try larger context: MarkB generic IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html