Greg Barnes Jonathan F. Buss Walter L. Ruzzo Baruch Schieber A Sublinear Space, Polynomial Time Algorithm for Directed <i>s</i>-<i>t</i> Connectivity. 1273-1282 1998 27 SIAM J. Comput. 5 http://dx.doi.org/10.1137/S0097539793283151 db/journals/siamcomp/siamcomp27.html#BarnesBRS98