@article{DBLP:journals/jacm/Klug82,
author = {Anthony C. Klug},
title = {Equivalence of Relational Algebra and Relational Calculus
Query Languages Having Aggregate Functions},
journal = {J. ACM},
volume = {29},
number = {3},
year = {1982},
pages = {699-717},
ee = {http://doi.acm.org/10.1145/322326.322332},
bibsource = {DBLP, http://dblp.uni-trier.de}
}