Boris N. Khoromskij Jens Markus Melenk An Efficient Direct Solver for the Boundary Concentrated FEM in 2D. 91-117 2002 69 2 Computing http://www.link.springer.de/link/service/journals/00607/bibs/2069002/20690091.htm db/journals/computing/computing69.html#KhoromskijM02