Now, note that for every formula_95, and for every formula_105, we have that formula_114, because when taking the partial derivative with respect to formula_115 of formula_116, we are keeping formula_117 fixed in the expression formula_118; thus the basic form of Leibniz's Integral Rule with constant limits of integration applies. Next, by the First Fundamental Theorem of Calculus, we have that formula_119; because when taking the partial derivative with respect to formula_117 of formula_116, the first variable formula_115 is fixed, so the fundamental theorem can indeed be applied.