Calogero quantum problem, Knizhnik–Zamolodchikov equation and Huygens principle

The interrelations between Calogero quantum problem and Knizhnik–Zamolodchikov equation are described following Matsuo, Cherednik, Felder and the author. As the basic tool of the considerations the Dunkl operator is used. The generalizations related to arbitrary Coxeter group and the applications to the Hadamard problem about the hyperbolic equations with the Huygens principle are discussed.