  The hexabasic book is the cone of the 1-dimensional skeleton of the union of
two tetrahedra glued along a common face. The universal 3-dimensional
polyhedron UP is the product of a segment and the hexabasic book. We show that
any 2-dimensional link in 4-space is isotopic to a surface in UP. The proof is
based on a representation of surfaces in 4-space by marked graphs, links with
double intersections in 3-space. We construct a finitely presented semigroup
whose central elements uniquely encode all isotopy classes of 2-dimensional
links.
