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Let $(u_1, u_2, u_3, u_4)$ and $(v_1, v_2, v_3, v_4)$ be vectors in $\mathbb R_+^4$. Is the following inequality true? (Matlab simulations did not yield a counterexample.)

\begin{align*} \left(\sum_{{4 \choose 3}} \sqrt{u_i u_j u_k}\right)^{2/3} + \left(\sum_{{4 \choose 3}} \sqrt{v_i v_j v_k}\right)^{2/3} \leq \left(\sum_{{4 \choose 3}} \sqrt{(v_i+u_i) (v_j+u_j) (v_k+u_k)}\right)^{2/3} \end{align*} Here $\sum_{{4 \choose 3}}$ refers to $\sum_{1\leq i < j < k \leq 4}$.

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  • $\begingroup$ If it's "Minkowski-like", shouldn't the relation rather be $\geq$? $\endgroup$ – Andreas Feb 14 '18 at 12:17

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