George Jaiani
I.Vekua Institute of Applied Mathematics
Iv.Javakhishvili Tbilisi State University
2 University st., Tbilisi 0143, Georgia
e-mail: jaiani@viam.sci.tsu.ge

Sergo kharibegashvili
A.Razmadze mathematical Institute
of the Georgian Academy of Sciences
1 M.Aleksidze st, Tbilisi 0193, Georgia
e-mail: khar@rmi.acnet.ge

David Natroshvili
Gergian Technical university
Department of Mathematics
77 M.Kostava st., Tbilisi 0175, Georgia
e-mail: natrosh@hotmail.com

Wolfgang L. Wendland
Mathematisches Institut A, Universitaet Stuttgart,
Pfaffenwaldring 57, D-70550 Stuttgart, Germany
e-mail: wendland@mathematik.uni-stuttgart.de