Definition talk:Angle

Is there a reference worthy approach somewhere that treats angles as equivalence classes? The equivalence relation being on $(\mathbb{R}^2)^3$. Likewise, for solid angles an equivalence relation on $(\mathbb{R}^3)^4$. --Jshflynn (talk) 17:50, 31 October 2012 (UTC)
I think I comprehend what you try to say. So $(x,y,z) \sim (x',y',z')$ iff the angles $yxz$ and $y'x'z'$ are equal. I haven't needed solid angles for a long time now, so I'm not entirely sure how you interpret $(\R^3)^4$. --Lord_Farin (talk) 19:54, 31 October 2012 (UTC)