It is generally believed that superconductivity only weakly affects the indirect exchange between
magnetic impurities. If the distance r between impurities is smaller than than the superconducting
coherence length (r≲ξ) , this exchange is thought to be dominated by RKKY interactions, identical
to the those in a normal metallic host. This perception is based on a perturbative treatment of
the exchange interaction. Here, we provide a non-perturbative analysis and demonstrate that the
presence of Yu-Shiba-Rusinov bound states induces a strong 1/r2 anti-ferromagnetic interaction that
can dominate over conventional RKKY even at distances significantly smaller than the coherence
length (r≪ξ). Experimental signatures, implications and applications are discussed.Physic