  The problem we are considering came up in connection with the classification
of singularities in positive characteristic. Then it is important that certain
invariants like the determinacy can be bounded simultaneously in families of
formal power series parametrized by some algebraic variety. In contrast to the
case of analytic or algebraic families, where such a bound is well known, the
problem is rather subtle, since the modules defining the invariants are
quasi-finite but not finite over the base space. In fact, in general the fibre
dimension is not semicontinuous and the quasi-finite locus is not open.
However, if we pass to the completed fibers in a family of modules we can prove
that their fiber dimension is semicontinuous under some mild conditions. We
prove this in a rather general framework by introducing and using the completed
and the Henselian tensor product, the proof being more involved as one might
think. Finally we apply this to the Milnor number and the Tjurina number in
families of hypersurfaces and complete intersections and to the determinacy in
a family of ideals.
