@article{HPV77,
AUTHOR = {Hopcroft, J.E. and Paul, W.J. and Valiant L.G.},
TITLE = {On Time Versus Space},
VOLUME = {24},
YEAR = {1977},
PAGES = {332--337},
SERIES = {J. ACM},
EE = {http://doi.acm.org/10.1145/322003.322015},
}