I found an inequality as following:
Let $x, y, z$ be three complex numbers then:
\begin{equation*} |y+z-x|+|x+z-y| + |y+x-z| \le |x| + |y|+|z|+|x+y+z|\end{equation*}
The inequality holds with equality if and only if $x+y+z=0$
My question: I am looking for a proof of a conjecture as following:
Let $x, y, z$ in an inner product space $V$ then
\begin{equation*}\|y+z-x\|+\|x+z-y\| + \|y+x-z\| \le \|x\| + \|y\|+\|z\|+\|x+y+z\|\end{equation*}
See also