Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that
| (i) | $E \subseteq X$ is a D249: F-sigma set in $T$ |
| (ii) | $X \setminus E$ is the D79: Set complement of $E$ within $X$ |
Then $X \setminus E$ is a D248: G-delta set in $T$.