I don't have any particular recipe [for developing new proofs] ... It is the reason why doing research is challenging as well as attractive. It's like being lost in a jungle and trying to use all the knowledge that you can gather to come up with some new tricks, and with some luck you might find a way out.
解释:既要追悔以往的过失,也要预防将来可能发生的错误。
Those who deny freedom to others, deserve it not for themselves; and, under a just God, can not long retain it.