A conjectured class of scale-invariant distances on inner product spaces
  Let $V$ be an inner product space, and $x, y \in V$; the conjecture is made that, for any $p \in [1, \infty]$, the function $d_p(x, y):=\|x-y\|/(\|x\|^p+ \|y\|^p)^{1/p}$ is a distance on $V$. 
Bruno Galvan
quant-ph math-ph math.FA math.MP