I understand the difference betw mathematical and physical pi. I also understand that in non-Euclidean space the value of pi would differ depending on a surface's deviation from flatness. But is there a different symbol for physical pi, to distinguish it from mathematical pi? Because I don't understand how pi works in the Einstein field equations (e.g., see: http://en.wikipedia.org/wiki/Einstein_field_equations) I'll ask a very naive question about these equations: does the pi in those equations have a variable value? in other words, if you were to replace pi with its mathematical value, would you get those equations wrong? ( or is there some part of the equations that makes pi change depending on curvature? or is there a different set of equations where pi variability is applicable??) I am trying to figure out how to properly answer someone who claims: "But pi shows up in Einstein's field equations, so how can you say pi doesn't quite apply in relativity?" I hope I have made my dilemma clear. I'd so very much appreciate help with this. I'm trying to explain these concepts to somebody (a case of the one-eyed leading the blind), and I don't want to misinform them. Thank you.