Paths are null-homotopic if they can be contracted to a point. The path in the clip is not null-homotopic, since it can not wiggle past the extra point.
This Video was produces for a topology seminar at the Leibniz Universitaet Hannover.
http://www-ifm.math.uni-hannover.de/~fugru/?topologie_teil1
This is one of your simpler videos :)
waffle12996 2 years ago