1. Aug 16, 2005

### dm368

how could v 'calculate' the orbifold euler char. using String theoriests' formula for the same ? For example, i know the Euler char. of S^1/Z_2 is 1, when we identify the x to -x points of S^1(not the antipodal points i.e. dimetrically opposite points, but putting a mirror along the horizontal line cutting the circle and identifying the mirror image points). But i don't know how to use the string theoreists' formula and don't get what summation over commutating group elements means(in S^1/Z_2 case, they are {1,-1} ).
S^2/Z_2 would be more elaborative perhaps ?
Thanks