Let $\mathcal{T}$ be a D86: Topology on $X$.
A D11: Set $\mathcal{S}$ is a subtopology of $\mathcal{T}$ on $X$ if and only if
(1) | $\mathcal{S} \subseteq \mathcal{T}$ (D78: Subset) |
(2) | $\mathcal{S}$ is a D86: Topology on $X$ |
(1) | $\mathcal{S} \subseteq \mathcal{T}$ (D78: Subset) |
(2) | $\mathcal{S}$ is a D86: Topology on $X$ |