In a paper translated from the Russian, the author refers to "m-m" and "n-n" circles (including Minkowski circles) and orbits. When I first came across "n-n", I thought it was "non-negative" until I came across the "m-m". In one of the references I went to a diagram referred to, and saw an arc with "n" on each end of the arc referred to as an "n-n unit circle". I have no idea what he is talking about. Is this some standard notation I am unfamiliar with, or some notation perhaps peculiar to Russian? In the same context, he has "m-m circles" with imaginary radii. I thought a radius was a distance, which is always real. ?? Thanks for guidance.