19 problems.
- Open balls in a metric space are open
- Continuity of the metric function
- A diagonal in the countable-closed and finite-complement topologies
- Relative openness in an open subspace
- Hausdorffness of the radial quotient of the open disk
- Compactness of the closed unit interval
- The real line is not compact
- Continuity of a coordinatewise map between products
- Closed subspaces of locally compact Hausdorff spaces
- The closure of a connected set is connected
- Connected components are connected
- Separating a closed set and a compact set in a regular space
- The equatorial embedding \(S^1\to S^2\) is homotopic to its reflection
- Path homotopy and simple connectedness
- The surface with polygonal symbol \(xyzx^{-1}zy^{-1}\), and classification of closed surfaces by even-sided polygons
- \(S^1\) is a retract of the Möbius band
- Simplicial homology of \(S^2\)
- Fundamental group of a sphere with three points removed
- Removing a point from a connected manifold of dimension at least 3