a. In your experience with proofs, is there a technique that was very difficult for you, or that seemed very anti-intuitive?

a.      In your experience with proofs, is there a technique that was very difficult for you, or that seemed very anti-intuitive?

b.      Explain how you confronted this technique in some context, with the statement, your level of mathematical maturity at that time (it could be very recent), the mathematical subject.

c.      Is there a specific "known" proof that you find difficult to understand, or to explain and develop?