@article(
MitchPlt,author="Mitchell, J.C. and Plotkin, G.D.", 
	Key="Mitchell and Plotkin 85",
	Title="Abstract types have existential types",
	Journal="ACM Trans. on Programming Languages and
	Systems", Volume="10",Number="3",Year="1988",
	pages="470-502",	
	Note="Preliminary version appeared in 
	{\it Proc. 12th ACM Symp. on Principles of 
	Programming  Languages,} 1985")