@article{Fekete_Varga_1977, title={On the formal definition of VDL-objects}, volume={3}, url={https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3149}, number={3}, journal={Acta Cybernetica}, author={Fekete, I. and Varga, L.}, year={1977}, month={Jan.}, pages={239-248} }