Is the consensus number of SetAgree(3, 2) 2 or 1 (proof needed)?
We can prove that 2-set-consensus among 3 processors (noted (3,2)) cannot be used (together with registers) to solve consensus among 2 processors (noted (2,1)) using the Borowsky-Gafni simulation (BG simulation for short).

The BG simulation allows 3 processors using registers only to simulate any algorithm in which 2 processors use registers and (3,2).
Therefore, the BG simulation transforms an algorithm A solving consensus among 2 processors using (3,2) into an algorithm B solving consensus among 3 processors using registers only.
Since the latter is impossible, there is no such algorithm A.

Note that by solving I mean solving wait-free.

This proof first appeared in Borowsky and Gafni, "Generalized FLP impossibility result for t-resilient asynchronous computations." Proceedings of the twenty-fifth annual ACM symposium on Theory of computing. ACM, 1993. (In particular see the end of section 3.3).