@article {Gumm:6 June 2001:0304-3975:57,
	author = "Gumm H.P.",
	title = "Equational and implicational classes of coalgebras",
	journal = "Theoretical Computer Science",
	volume = "260",
	year = "6 June 2001",
	abstract = "",
	pages = "57-69(13)",
	url = "http://www.ingentaconnect.com/content/els/03043975/2001/00000260/00000001/art00122"
	doi = "doi:10.1016/S0304-3975(00)00122-5"
}