abstract = "Coevolution often gives rise to counter-intuitive
dynamics that defy our expectations. Here we suggest
that much of the confusion surrounding co-evolution
results from imprecise notions of superiority and
progress. In particular, we note that in the
literature, three distinct notions of progress are
implicitly lumped together: local progress (superior
performance against current opponents), historical
progress (superior performance against previous
opponents) and global progress (superior performance
against the entire opponent space). As a result, valid
conditions for one type of progress are unduly assumed
to lead to another. In particular, the confusion
between historical and global progress is a case of a
common error, namely using the training set as a test
set. This error is prevalent among standard methods for
coevolutionary analysis (CIAO, Master Tournament,
Dominance Tournament, etc.) By clearly defining and
distinguishing between different types of progress, we
identify limitations with existing techniques and
algorithms, address them, and generally facilitate
discussion and understanding of co-evolution. We
conclude that the concepts proposed in this paper
correspond to important aspects of the coevolutionary
process.",