Grigori Perelman

In June 2006 Yau's students Xi-Ping Zhu and Huai-Dong Cao published a paper, filling the entire June 2006 issue of the Asian Journal of Mathematics which Yau co-edits, describing itself as completing the proof of the Poincare and geometrization conjectures. At a Beijing press conference the acting director of Yau's own mathematics institute credited Hamilton with over fifty percent, Perelman with about twenty five percent, and Yau, Zhu and Cao with about thirty percent, a division that does not even sum to one hundred. Yau said in a public lecture that in Perelman's work many key ideas were sketched or outlined with complete details often missing, and that Zhu and Cao's paper was a complete solution to the puzzle. Other mathematicians disputed this characterization at the time: John Morgan said Perelman had already done it and that his proof was complete and correct, and that he did not see that Zhu and Cao had done anything different; Perelman himself, asked about the Zhu-Cao paper, said it was not clear to him what new contribution they had made, and that Zhu appeared not to have quite understood the argument and reworked it.