Serafino Cicerone Daniele Frigioni Umberto Nanni Francesco Pugliese A Uniform Approach to Semi-Dynamic Problems on Digraphs. 69-90 1998 203 Theor. Comput. Sci. 1 db/journals/tcs/tcs203.html#CiceroneFNP98 http://dx.doi.org/10.1016/S0304-3975(97)00288-0