@Article{	  mp96,
  author	= "Anca Muscholl and Holger Petersen",
  title		= "A Note on the Commutative Closure of Star-Free Languages",
  journal	= "Information Processing Letters",
  year		= "1996",
  volume	= "57",
  number	= "2",
  pages		= "71--74",
  doi		= "10.1016/0020-0190(95)00187-5"
}