GREG KNESE, SCHUR-AGLER CLASS RATIONAL INNER FUNCTIONS ON THE TRIDISK, Proceedings of the American Mathematical Society, Vol. 139, No. 11 (NOVEMBER 2011), pp. 4063-4072 ...

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 ...