Interactive pages for Algebraic Topology

Various surfaces
A cube with holes
Trefoil knot
Folding a square to make a torus
The torus as a quotient of the plane
Letters of the alphabet
Letters grouped by type
Cage with two or three holes
Barycentric coordinates
Different triangulations of the sphere
The triangle and the square
Skeleta of simplices
Open sets
Finite element model
A cylinder is homeomorphic to an annulus
Stereographic projection
$\mathbb{R}P^1$ is homeomorphic to $S^1$
Gluing two discs to make a sphere
Loops on the sphere
Loops on the torus
A homotopy of the trefoil
Geometry of the Möbius strip
The Möbius strip and the circle
The punctured plane
The punctured sphere
The punctured torus
Wrapping an annulus
The exponential map
The exponential map is a covering
Path lifting
Homotopy lifting
Subdivision of a prism $[0,1]\times\Delta_2$
Boundary of a tetrahedron
Barycentric subdivision of a tetrahedron
The map $\mu\colon|K'|\to|K|$