@article{ harper+:lf-jacm,
author	=	"Robert Harper and Furio Honsell and Gordon Plotkin" ,
title	=	"A Framework for Defining Logics" ,
journal	=	"Journal of the Association for Computing Machinery" ,
volume	=	"40" ,
number	=	"1" ,
month	=	"January" ,
year	=	"1993" ,
pages	=	"143--184"
}