Krzysztof Diks Torben Hagerup More General Parallel Tree Contraction: Register Allocation and Broadcasting in a Tree. 3-29 1998 203 Theor. Comput. Sci. 1 db/journals/tcs/tcs203.html#DiksH98 http://dx.doi.org/10.1016/S0304-3975(97)00285-5