Def mapcons(f;as) == Case of as; nil  nil ; a.as'  f(a,as').mapcons(f;as')
Def (recursive)

is mentioned by

Def ForHdTl{A,f,k} h::t  as. g(h;t) == reduce(f;k;mapcons(h,t. g(h;t);as))

[for_hdtl]

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