Hi Doug and Johan:

I just thought about the following algorithm for checking
compatability of two graphs. Does something like this work? 

If for a path in the strategy graph there is no expanding path
in the class graph then there must be a single edge in the
strategy graph which does not have an expanding path in the class graph.

If each strategy graph edge has an expanding path then
also each strategy graph path has an expanding path.

Therefore, for checking compatability we check for each strategy
graph edge S = {X->Y} with source X and target Y whether
PathSet[G](S) is non-empty. This amounts to computing
n times a propagation graph where n is the number
of strategy graph edges. Clearly efficient. Is there
a faster way?

Johan: make this a part of the technical report and question list
for Boaz.

-- Karl