On Certain Special Solutions of the \Phi-Equation of Statistical Hydrodynamics Eberhard HopfE. Titt Indiana University Mathematics Journal 1953 text pdf 10.1512/iumj.1953.2.52029 10.1512/iumj.1953.2.52029 en Indiana Univ. Math. J. 2 (1953) 587 - 591 state-of-the-art mathematics http://iumj.org/access/