  We predict the energy per baryon in nuclear matter with non-zero fraction of
$\Lambda$ hyperons. We include Dirac effects on the nucleons as well as the
$\Lambda$ and describe how the latter is implemented. We use the
nucleon-hyperon meson-exchange potentials from the Juelich group, the latest as
well as an earlier version. The dependence of the results on the many-body
framework and on the nucleon-hyperon interaction model is discussed.
