  Thanks: As I remember, I saw O/O referred to as an undefined number, which I changed to read 1/0. O/O = 0, as does 0/1; whereas 1/0 is an undefined number;I gave my source as  p 25 of Ballou & Steen's PLANE & SPHERICAL TRIGONOMETRY WITH  LES,second edition. The re-edited version goes towards this, but has  the bizarre notation of infinity inverted, an affectation that obscures understanding the matter. 0/0 No part of nothing, 1/0 some part of nothing; 0/1 no part of something. Infinity is not nothing.   