The Sum Formula of Multiple Zeta Values and Connection Problem of the Formal Knizhnik-Zamolodchikov Equation

The sum formula for multiple zeta values are derived, via the Mellin transform, from the Euler connection formula and the Landen connection formula for polylogarithms. These connection formulas for multiple polylogarithms will be considered in the framework of the theory of the formal Knizhnik-Zamolodchikov equation.