| context | $\langle X,\mathcal{T}_X\rangle, \langle Y,\mathcal{T}_Y\rangle$ … topological spaces |
| definiendum | $f\in$ it |
| inclusion | $f$ … bijection, continuous |
| postulate | $f^{-1}$ … continuous |
A homeomorphism is a bijection which is continuous in both directions.
Wikipedia: Homeomorphism