source:Source: https://www.cambridge.org/core/services/aop-cambridge-core/content/view/5035A2A741F2757B6C1242A000BC7A12/S0013091500011214a.pdf/div-class-title-some-inequalities-involving-span-class-italic-r-span-span-class-sup-1-span-class-italic-r-span-span-div.pdf
