I am looking for a proof of the Huppert's Theorem (1954): "Every maximal subgroup of a finite group has prime index. So $G$ is supersoluble". The proof on Robinsone is hard for me, and i found another one on this link(page 30): http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.28.2482&rep=rep1&type=pdf
But I don't understand the last part very well. Where can I find one which is not too difficult? Thanks