ADerivation of time-evolving attention operators

We show the full derivation of Equation 6 as follows. Recall that X0i is the concatenation of Xi and Tl. The model variation used here in TransEvolve-fullFF. Thus, on the limiting case, we get E[Ul(Ul)>] = 1I where I is the d-dimensional identity matrix. This way, Ul2 dd approximates a rotation matrix as we choose σ = O(d).