  Hybrid and mixed strategy EAs have become rather popular for tackling various
complex and NP-hard optimization problems. While empirical evidence suggests
that such algorithms are successful in practice, rather little theoretical
support for their success is available, not mentioning a solid mathematical
foundation that would provide guidance towards an efficient design of this type
of EAs. In the current paper we develop a rigorous mathematical framework that
suggests such designs based on generalized schema theory, fitness levels and
drift analysis. An example-application for tackling one of the classical
NP-hard problems, the "single-machine scheduling problem" is presented.
