Hello! I am reading a derivation for Fermi pressure and the author assumes that the electrons in a box are cooled so much that they occupy all the states in the momentum space from p=0 up to a maximum value of p. Then after he obtains a formula for the pressure, he simplifies the formula further, by assuming a very relativistic gas. I am not sure I understand how can we make both assumptions. If we reduce it as much as we can (basically close to 0K), it means that the velocities are very small (the temperature is given by the speed of the particles, so small temperature means small speed). So if the velocities are small, how can one assume "very relativistic" conditions? Thank you!