Let XX be a real , and let Ω1,Ω2X\Omega_1,\Omega_2\subseteq X be nonempty . If

core(Ω1)andΩ1Ω2=,\operatorname{core}(\Omega_1)\neq\varnothing \qquad\text{and}\qquad \Omega_1\cap\Omega_2=\varnothing,

then Ω1\Omega_1 and Ω2\Omega_2 can be .

Remarks

The proof reduces separation of two sets to separation of a point from a convex set by applying to the Minkowski difference Ω1Ω2\Omega_1-\Omega_2.