I guess then the question is "what is F". That is, what does the function F represent in that formula? Are the subscripts indices or derivatives? And if they are derivatives, what do F' and F'' mean?

I guess then the question is "what is F". That is, what does the function F represent in that formula? Are the subscripts indices or derivatives? And if they are derivatives, what do F' and F'' mean?

well that is what i wonder too..I got that formula from Bronstein's handbook of mathematics, as a formula for curvature, but i don't really understand anything about it =(((