Def spanner-root(f;T;to;from;i) == l:Edge(T). (l  to(i))  (f(l))

is mentioned by

Thm* T:(Id), to,from:(|T|(IdLnk List)), f:(Edge(T)). Thm* bi-tree(T;to;from) Thm*  Thm* spanner(f;T;to;from) Thm*  Thm* (i,j:|T|. Thm* (spanner-root(f;T;to;from;i)  spanner-root(f;T;to;from;j)  i = j)	[spanner-root-unique]
Thm* T:(Id), to,from:(|T|(IdLnk List)), f:(Edge(T)). Thm* bi-tree(T;to;from) Thm*  Thm* spanner(f;T;to;from)  (i:|T|. spanner-root(f;T;to;from;i))	[spanner-root-exists]

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