1. Faculty of Civil Engineering, Technical University Cluj-Napoca, 72 Observatorului Street, 400641 Cluj-Napoca, Romania
2. Department of Economics and Physics, Faculty of Sciences, Technical University Cluj-Napoca, 76 Victoriei Street, 430122 Baia-Mare, Romania
3. Faculty of Geodesy and Cartography, Warsaw University of Technology, Plac Politechniki 1, 00-661 Warsaw, Poland
4. Department of Algebra and Differential Equations, Uzhhorod National University, 3 Narodna Square, Transcarpathian Region, 88000 Uzhhorod, Ukraine