Yaacov Choueka Aviezri S. Fraenkel Shmuel T. Klein E. Segal Improved Hierarchical Bit-Vector Compression in Document Retrieval Systems. 88-96 1986 SIGIR db/conf/sigir/sigir86.html#ChouekaFKS86 conf/sigir/86 SIGIR1986/P088.pdf db/conf/sigir/ChouekaFKS86.html