[IEEE Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory. Proceedings of 4th International Seminar/Workshop. DIPED - 99 - Lviv, Ukraine (1999.9.20-1999.9.23)] DIPED - 99. Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory. Proceedings of 4th International Seminar/Workshop (IEEE Cat. No.99TH8402) - Legendre polynomials as finite elements in boundary integral equations for transmission problem with periodic piecewise-linear boundary