Steven W. Reyner An Analysis of a Good Algorithm for the Subtree Problem. 730-732 1977 6 SIAM J. Comput. 4 db/journals/siamcomp/siamcomp6.html#Reyner77 http://dx.doi.org/10.1137/0206053 Correction: SIAM J. Comput. 18(5): 906-908 (1989)