  A Green functions approach is used to study superconductivity in nanofilms
and nanowires. We show that the superconducting condensate results from the
multimodal entanglement, or internal Josephson coupling, of the subcondensates
associated with the manifold of Fermi surface subparts resulting from
size-quantisation. This entanglement is of critical importance in these
systems, since without it superconductivity would be extremely weak, if not
completely negligible. Further, the multimodal character of the condensate
generally results in multigap superconductivity, with great quantitative
consequence for the value of the critical parameters. Our approach suggests
that these are universal characteristics of confined superconductors.
