@Article{	  die86tcsb,
  author	= "Volker Diekert",
  journal	= "Theoretical Computer Science",
  pages		= "319--327",
  title		= "Commutative monoids have complete presentations by free
		  (non-commutative) monoids",
  volume	= "46",
  year		= "1986",
  doi		= "10.1016/0304-3975(86)90037-X"
}