Def spanner(f;T;to;from)
Def == (l:Edge(T). f(l) = f(inverse(l)))
Def == & (i:|T|, l1,l2:Edge(T).
Def == & ((l1  to(i))
Def == & (
Def == & ((l2  to(i))  l1 = l2  IdLnk  (f(l1))  (f(l2)))

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