Intermediate and extrapolated spaces for bi-continuous semigroups

We discuss the construction of the full Sobolev (H"older) scale for non-densely defined operators on a Banach space with rays of minimal growth. In particular, we give a construction for extrapolation- and Favard spaces of generators of (bi-continuous) semigroups, or which is essentially the same, Hille-Yosida operators on Saks spaces.