Takakazu Mori Mariko Yasugi Yoshiki Tsujii Integral of Two-dimensional Fine-computable Functions. 141-152 2008 221 Electr. Notes Theor. Comput. Sci. http://dx.doi.org/10.1016/j.entcs.2008.12.013 db/journals/entcs/entcs221.html#MoriYT08a