@ARTICLE{Li+HuangETAL-Stabanalpenaplus:07,
  author       = {Li, Z. C. and Huang, H. T. and Huang, J. and Ling, L.},
  title        = {Stability analysis for the penalty plus hybrid and the direct {T}refftz methods for singularity problems},
  journal      = {Eng. Anal. Bound. Elem.},
  fjournal     = {Engineering Analysis with Boundary Elements},
  volume       = {31},
  number       = {2},
  pages        = {163-175},
  year         = {2007},
}