[see also: set
Neighbourhoods of points in these spaces appear at first glance to have a nice regular structure, but upon closer scrutiny, one sees that many neighbourhoods contain collections of arcs hopelessly folded up.
Continuing in this fashion, we get a collection {Vr} of open sets, one for every rational r, with......
Next we relabel the collection {An,Bn} as {Cn}.
The words collection, family and class will be used synonymously with set.
The theorem implies that some finite subcollection of the fi can be removed without altering the span.