Hello, I have been trying to work out the mathematical details of H Snyder's 1947 paper, titled "http://prola.aps.org/abstract/PR/v71/i1/p38_1" [Broken], and I am stuck at something. When the space-time variables are considered as Hermitian operators, and we need to verify that they satisfy Lorentz invariance, I believe we need the quantity speed in the Lorentz transformation equations. My question is, in the context of Snyder's paper, how do we define speed? Further, if speed is not required, then how do we prove the Lorentz invariance of these operators? Please do guide me on this, if you have an idea of what I am talking about. Thank you.