Let XX be a and let Ω⊂X\Omega\subset X be .

Corollary:

core⁡(core⁡(Ω))=core⁡(Ω).\operatorname{core}(\operatorname{core}(\Omega))=\operatorname{core}(\Omega).

Here denotes the algebraic interior.

Remarks

This follows from : once a point is in core⁡(Ω)\operatorname{core}(\Omega), small segment perturbations remain inside, so taking the core again does not remove any points.