  For any simplicial complex on m vertices a moment-angle complex Z_K embedded
in C^m can be defined. There is a canonical action of a torus T^m on Z_K, but
this action fails to be free. The Buchstaber number is the maximal integer s(K)
for which there exists a subtorus of rank s(K) acting freely on Z_K. The
similar definition can be given for real Buchstaber number. We study these
invariants using certain sequences of simplicial complexes called universal
complexes. Some general properties of Buchstaber numbers follow from
combinatorial properties of universal complexes. In particular, we investigate
the additivity of Buchstaber invariant.
