Def Y(f) == (x.f(x(x)))(x.f(x(x)))

is mentioned by

Def mapc(f)(as) == Case of as; nil  nil ; a.as1  f(a).mapc(f)(as1) Def (recursive)	[mapc]
Def f{m..n} == if nm nil else f(m).f{(m+1)..n} fi  (recursive)	[listify]
Def mapcons(f;as) == Case of as; nil  nil ; a.as'  f(a,as').mapcons(f;as') Def (recursive)	[mapcons]
Def reduce(f;k;as) == Case of as; nil  k ; a.as'  f(a,reduce(f;k;as')) Def (recursive)	[reduce]
Def as\[i] Def == if i0 tl(as) else Case of as; nil  nil ; a'.as'  a'.as'\[i-1] fi Def (recursive)	[reject]
Def firstn(n;as) Def == Case of as; nil  nil ; a.as'  if 0<n a.firstn(n-1;as') else nil fi Def (recursive)	[firstn]
Def rev(as) == Case of as; nil  nil ; a.as'  rev(as') @ [a]  (recursive)	[reverse]
Def nth_tl(n;as) == if n0 as else nth_tl(n-1;tl(as)) fi  (recursive)	[nth_tl]
Def map(f;as) == Case of as; nil  nil ; a.as'  f(a).map(f;as')  (recursive)	[map]
Def ||as|| == Case of as; nil  0 ; a.as'  ||as'||+1  (recursive)	[length]
Def as @ bs == Case of as; nil  bs ; a.as'  a.(as' @ bs)  (recursive)	[append]

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