The interrelations between Calogero quantum problem and Knizhnik-Zamol
odchikov equation are described following Matsuo, Cherednik, Felder, a
nd the author. As the basic tool of the considerations the Dunkl opera
tor is used. The generalizations related to an arbitrary Coxeter group
and the applications to the Hadamard problem about the hyperbolic equ
ations with the Huygens principle are discussed.