[math-fun] Addition formula paper

I'm looking for a paper I read once (more than six years ago) on addition formulas. It had the tangent addition formula as a special case: atan(x) + atan(y) = atan((x+y)/(1-xy)) as well as log log(x) + log(y) = log(xy) and various other ones. The idea was to find a function p and an operator @ such that p(x) + p(y) = p(x@y), and they showed how to come up with a large class of these. It also, as I recall, had something to do with intersecting chords of a conic. Does anyone know what paper this was, or could anyone suggest keywords to google for it? -- Mike Stay - metaweta@gmail.com http://math.ucr.edu/~mike http://reperiendi.wordpress.com