[4] A. A. Abrikosov. On the magnetic properties of superconductors of the second group. Sov. Phys. JETP, 5, 1174-1183(1957).
[17] D. Sugic, M. R. Dennis. Singular knot bundle in light. J. Opt. Soc. Am. A, 35, 1987-1999(2018).
[25] I. Freund. Polarization singularities in optical lattices. Opt. Lett., 29, 875-877(2004).