  Recent success of Low Energy RHIC Electron Cooler (LEReC) opened a road for
development of high energy electron coolers based on non-magnetized electron
bunches accelerated by RF cavities. Electrons in such coolers can have velocity
distribution with various unequal horizontal, vertical and longitudinal
velocity spreads. In this paper we revisit a formula of friction force in
non-magnetized cooling and derive a number of useful expressions for different
limiting cases.
