@article{Łenski:2008,
  author  = "W. Łenski and B. Szal",
  title   = "Pointwise strong and very strong approximation by matrix means of Fourier series",
  journal = "Annales Societatis Mathematicae Polonae : Commentationes Mathematicae : Series I",
  volume  = "Vol. 48",
  number  = "no 2",
  pages   = "177--198",
  year    = "2008",
}