Complex Separation Theorem (Real Parts)

In complex vector spaces, separation holds via the real part of a complex linear functional.
Complex Separation Theorem (Real Parts)

Let XX be a complex and let Ω1,Ω2X\Omega_1,\Omega_2\subset X be nonempty . Assume \neq\emptyset and core(Ω1)Ω2=\operatorname{core}(\Omega_1)\cap\Omega_2=\emptyset.

Theorem: There exists a nonzero complex-linear functional FF on XX such that

ReF(x)ReF(y)whenever xΩ1, yΩ2. \operatorname{Re}F(x)\le \operatorname{Re}F(y)\quad\text{whenever }x\in\Omega_1,\ y\in\Omega_2.

Context: View XX as a real vector space and apply to obtain a real linear functional ff. Then form a complex functional FF whose real part is ff.