\sum_{k=1}^{n}{|x_ky_k|}\le \left(\sum_{k=1}^{n}|x_k|^p\right)^{\frac{1}{p}}\left(\sum_{k=1}^{n}|y_k|^q\right)^{\frac{1}{q}}, \frac{1}{p}+\frac{1}{q}=1