Identities in plactic, hypoplactic, sylvester, Baxter, and related   monoids
  This paper considers whether non-trivial identities are satisfied by certain `plactic-like' monoids that, like the plactic monoid, are closely connected to combinatorics. New results show that the hypoplactic, sylvester, Baxter, stalactic, and taiga monoids satisfy identities, and indeed give shortest identities satisfied by these monoids. The existing state of knowledge is discussed for the plactic monoid and left and right patience sorting monoids. 
Alan J. Cain, Ant\'onio Malheiro
math.CO math.GR