There is not yet a built-in way to get (sub)sets of the nodes of an extensive game. Some ideas:

• Game.nodes returns a collection of nodes. Presumably this should be implemented implicitly - it should return an e.g. NodeSet object rather than an explicit list of nodes.
• This NodeSet should define the ability to filter on a boolean function. Possibly getitem should be used for this (which would be similar to pandas indexing), although perhaps a .filter() member could be defined instead.

This might then combine well with #188 (nodes as histories) in building games - as it would be easy e.g. to filter on "all terminal nodes with histories matching a particular pattern".