Abstract (EN)

I hope the problems of the list below might be useful even for beginners, being however open and allowing both experimental discoveries of new facts and creation of general theories. They represent my seminar talks at Moscow in September 2003 and at Paris in January 2004. I'm grateful to many participants of these seminars for active work on these problems and for their help, especially for the many remarks of F. Aicardi and of R. Uribe-Vargas, responsible for the typing at the Paris part.