“…Existence itself of the ideal-hydrodynamic solutions in the form of quasi-one-dimensional vortex structures (vortex filaments) filling just a small part of the total fluid bulk is closely connected with the freezing-in property of the vortex lines [1,2,3,4,5,6,7,8,9,10,11,12,13]. Mathematically this property is expressed by the special form of the equation of motion for the divergence-free vorticity field Ω(r, t) = curl v(r, t),…”