In pursuance of this aim the author has considered it desirable to quote extensively from the works of the mathematicians of bygone days, for in that way alone can a just appraisal of the great difficulties under which they laboured be made.

• 为此目的，作者认为不妨从过去的数学家的著作中大量摘引。唯有如此，才能对他们经历的巨大困难作出正确的评价。