Pinched torus

Definition
The torus pinched at a point, or pinched torus, can be viewed in the following ways:


 * It is the one-point compactification of the open cylinder
 * It is the quotient of the torus by collapsing one of the sectional circles to a point
 * It is the quotient of the sphere by identifying two distinct points

Covering spaces
The universal covering space of the pinched torus is the pinched helix, which is homotopy-equivalent to a countable wedge of 2-spheres.