Ref: Professor Stewart’s Cabinet of Mathematical Curiosities by Ian Stewart.
Don’t Let Go!
Topology is a branch of mathematics in which two shapes are the same if one can be continuously deformed into the other, so you can bend, stretch, and shrink, but not cut. This topological chestnut still has many attractions — in particular, not everyone has seen it before. What you have to do is pick up a length of rope, with the left hand holding one end and the right hand holding the other, and tie a knot in the rope without letting go of the ends.
More later,
Nalin Pithwa
PS: A topologist cannot differentiate between a coffee cup and a dough-nut !! I think there are some nice videos of these on the internet.
Mathematics Hothouse 