@article(
HarperMitch,author="Harper, R. and Mitchell, J.C.", 
        Title="On the type structure of {Standard ML}",
        Journal="ACM Trans. Programming Lang. and Systems",
        volume="15",Number="2",Year="1993",pages="211--252",
        Note={Earlier version appears as
        ``The Essence of {ML}'' in 
        {\it Proc. 15th ACM Symp. on Principles of 
        Programming  Languages,}
        1988, pp. 28--46})