Corrected definition of Voronoi Cell, and other small changes
Typos
Basics on Fourier series

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>
Merge remote-tracking branch 'kivantos/master'

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>