In each manifold
modeled on a finite- or infinite-dimensional cube
,
, we construct a closed
nowhere dense subset
(called a spongy set) which is a universal nowhere dense set in
in the sense that for each nowhere dense subset
there is a
homeomorphism
such that .
The key tool in the construction of spongy sets is a theorem on the topological
equivalence of certain decompositions of manifolds. A special case of this
theorem says that two vanishing cellular strongly shrinkable decompositions
of a Hilbert
cube manifold
are topologically equivalent if any two nonsingleton elements
and
of
these decompositions are ambiently homeomorphic.
Keywords
Universal nowhere dense subset, Sierpiński carpet, Menger
cube, Hilbert cube manifold, $n$–manifold, tame ball, tame
decomposition
Department of Geometry and
Topology
Ivan Franko National University of Lviv
1 Universytetska str
Lviv, 79000
Ukraine
and
Instytut Matematyki
Jan Kochanowski University in Kielce
15 Swietokrzyska str
25-406 Kielce
Poland