Recall that a kernel conditionaly of negative type on a set $X$ is a map $psi:Xtimes Xrightarrowmathbb{R}$ with the following properties:
1) $psi(x,x)=0$
2) $psi(y,x)=psi(x,y)$
3) for any elements $x_1,...x_n$ and all real numbers $c_1,...,c_n$, with $c_1+...+c_n=0$, the following inequality holds:
$$
sum_{i=1}^{n}sum_{j=1}^{n}
c_ic_jpsi(x_i,x_j)leq 0.
$$
Let $G$ be a discrete group.
Recall that a function $Grightarrow mathbb{R}$ is conditionally of
negative type if the kernel $psi$, defined by $psi(g,h)= psi(h^{−1}g)$ is conditionaly of negative type.
Does there exist class of discrete groups which admit an explicit description of functions which are conditionaly of negative type?
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