  We consider the dimensional crossover in the topological matter, which
involves the transformation of different types of topologically protected
zeroes in the fermionic spectrum. In the considered case, the multiple Dirac
(Fermi) point in quasi 2-dimensional system evolves into the flat band on the
surface of the 3-dimensional system when the number of atomic layers increases.
This is accompanied by formation of the spiral nodal lines in the bulk. We also
discuss the topological quantum phase transition at which the surface flat band
shrinks and changes its chirality, while the nodal spiral changes its helicity.
