Consensus number of memory-to-memory swap
See Theorem 10 (Figure 13) of the paper "Wait-Free Synchronization
" by Herlihy, 1991.


  Theorem 10: An array of registers with memory-to-meory swap has infinite
  consensus number.
  
  Proof: The protocol is shown in Figure 13. The processes share an array of
  registers $a[1 \ldots n]$ whose elements are initialized to $0$ and a single register $r$, initialized to $1$. The first process to swap $1$ into $a$ wins.




Footnote 4 of this paper remarks that: 


  The memory-to-memory swap should not be confused with the read-modify-write swap; the former exchanges the values of two public registers, while the latter exchanges the value of a public register with a processor’s private register.