\[\int_{a}^{b}\,\mathrm{d}x_{n}\int_{a}^{x_{n}}\,\mathrm{d}x_{n-1}\cdots\int_{a}%
^{x_{2}}\,\mathrm{d}x_{1}\int_{a}^{x_{1}}f(x)\,\mathrm{d}x=\frac{1}{n!}\int_{a%
}^{b}(b-x)^{n}f(x)\,\mathrm{d}x.\]