@article{Kahlig:1996,
  author  = "P. Kahlig and J. Matkowski",
  title   = "Envelopes of special class of one-parameter families of curves",
  journal = "Demonstratio Mathematica",
  volume  = "Vol. 29",
  number  = "no 4",
  pages   = "799--806",
  year    = "1996",
}