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.
There is a stubbornness about me that never can bear to be frightened at the will of others. My courage always rises at every attempt to intimidate me.