The ( G ' / G ) -expansion method for solving the combined and the double combined sinh-cosh-Gordon equations. Kheiri, H., Jabbari, A. (2010) Acta Universitatis Apulensis. Mathematics - Informatics
The symbol of a lagrangian distribution Dimitri G. Vassiliev (1995) Journées équations aux dérivées partielles
Time-evolution of a caustic. Ari, Nasit, Gorman, Arthur D. (1988) International Journal of Mathematics and Mathematical Sciences