This is equivalent to the following result: If all critical points of a rational function lie on a circle in the Riemann sphere (for example, on the real line), then the function maps this circle into ...

JIE SHEN, LI-LIAN WANG, HUIYUAN LI, A TRIANGULAR SPECTRAL ELEMENT METHOD USING FULLY TENSORIAL RATIONAL BASIS FUNCTIONS, SIAM Journal on Numerical Analysis, Vol. 47, No. 3 (2009), pp. 1619-1650 ...