“…The additional scalar (dressing) factor [6] is constrained by the Hopf-algebraic analog of crossing symmetry [7]. Remarkable advances in the exact determination of this phase factor have been recently made [8,9], as well as progress in understanding the nature of the infinite dimensional symmetry algebra underlying the planar integrability of the model [10,11,12]. In [13], in particular, a Yangian symmetry has been advocated, and the hope for the existence of a universal R-matrix which could reproduce the AdS/CFT scattering matrix upon choosing an appropriate representation, has been put on somewhat firmer grounds.…”