Some answers in stackexchange too: http://math.stackexchange.com/questions/6136/is-there-a-mathematical-theorem-that-states-the-equivalence-of-curved-and-straig

Some answers in stackexchange too: http://math.stackexchange.com/questions/6136/is-there-a-mathematical-theorem-that-states-the-equivalence-of-curved-and-straigh http://math.stackexchange.com/questions/6136/is-there-a-math...