I am studying Knot theory and have gone through the Wirtinger Presentation for the Knot Group. However, I come across the different(at least for me) way of finding the Knot Group. Instead of labeling curves Bela Bollobas is labeling the closed region and then come up with the presentation $$<a,b,c,d \mid ad^{-1}b, cd^{-1}a, cbd^{-1}>$$
I didn't get how this presentation we got with the given labeling, or I say what is this method called and how we write presentation of knot group via this method.