We compare the physical potential VD(R) of an external quark-antiquark
pair in the representation D of SU(N), to the color-Coulomb potential Vcoul(R) which is the instantaneous part of the 44-component of the gluon
propagator in Coulomb gauge, D_{44}(\vx,t) = V_{\rm coul}(|\vx|) \delta(t) +
(non-instantaneous). We show that if VD(R) is confining, limR→∞VD(R)=+∞, then the inequality VD(R)≤−CDVcoul(R) holds asymptotically at large R, where CD>0 is the Casimir in
the representation D. This implies that −Vcoul(R) is also
confining.Comment: 9 page