Kantorovich–Rubinstein theorem
= Kantorovich–Rubinstein theorem
{c}
On a <Polish space> $(X,\rho)$, <probability measures> with finite first <moments> satisfy
$$
W_1(\mu,\nu)=\sup_{\operatorname{Lip}(f)\leq1}\left(\int f\,d\mu-\int f\,d\nu\right).
$$
The supremum runs over functions with <Lipschitz constant> at most one. Fixing $f(x_0)=0$ ensures integrability from the moment assumption.