Somewhat related: http://www.math.upenn.edu/~ghrist/notes.html http://www.math.upenn.edu/~ghrist/notes.html (and somewhat more high-brow, but still with a disc

Somewhat related: http://www.math.upenn.edu/~ghrist/notes.html http://www.math.upenn.edu/~ghrist/notes.html (and somewhat more high-brow, but still with a discrete flavour.)