Hi Johan:

does the following theorem hold?
How would you prove it?

This is needed to decide whether a strategy is of a certain strategy
type.

-- Karl
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Definition:
A strategy s1 is a substrategy of strategy s2, if 
for all class graphs G:
PathSet[G](s1) is a subset of PathSet[G](s2).

Theorem:
s1 is a substrategy of s2 iff PathSet[s1](s2) is not empty.

-- Karl