Hyperbolic case   I cant make sense of the following  In hyperbolic geometry for a right triangle one can also write    where  is the angle of parallelism of the line segment AB that  where  is the multiplicative distance function see Hilberts arithmetic of ends   The sentence doesnt quite parse   Is  really related to the segment AB rather than to BC That is weird notation  Why are we told about  even though a doesnt even show up in the formula  In the sequel the letters a b and c are used Are they still the ordinary side lengths of the right triangle as in the rest of the article