@inproceedings{KKY97,
	author	    =   "O. Kupferman and R.P. Kurshan and M. Yannakakis",
        title       =   "Existance of reduction hierarchies", 
        booktitle   =   "Proc. Annual conference of the {E}uropean
                         Association for computer Science Logic",
        address     =   "Aarhus",
        month       =   "August",
        year        =   "1997",
}