Hilbert's third problem. The equality of the volumes of two tetrahedra of
equal bases and equal altitudes. Solved in the negative sense by Hilbert's
student M. Dehn (actually before Hilbert's lecture was delivered, in 1900;
嚓，老希这。。。是不是故意的？？拿个小插曲课题跟黎曼猜想这些并列，还放水给自
己学生。。。
