@workingPaper{DoniniHollunderLenzeriniSpaccamelaNardNutt_1991, title={The complexity of existential quantification in concept languages}, author={Donini, Francesco M. and Hollunder, Bernhard and Lenzerini, Maurizio and Spaccamela, Alberto Marchetti and Nard, Daniele and Nutt, Werner}, doi={http://dx.doi.org/10.22028/D291-24836}, year={1991} }