Back in my undergrad days, there was a second year course titled "Groups, Rings and Modules". The lecturer (NSB) was notorious for his very dense and formal delivery, which left a lot of work to the reader. Another - much more popular - professor (IL) decided to offer an alternative version of the course during the same timeslots in a friendlier style. Despite NSB's absent-minded nature, it cannot have escaped his attention that ~10 people attended his lectures while the bulk of the year group queued up outside a different hall. Some friends and I attended NSB's lectures out of bloody-mindedness. We anticipated (correctly, it turns out) that if you managed to understand his notes, then you really understood the topic.
The reason I'm reminded of this is that one of the big theorems of the course is the simplicity of A5. I vaguely remember that NSB provided the icosahedron-based proof that's mentioned in the linked article, whereas IL provided a more intuitive and sensible proof.
One of the perks of being the official lecturer is that you set the exam questions. Imagine our delight when we opened the paper and saw the question: "By considering the rotations of an icosahedron, prove that the group A5 is simple"!
The reason I'm reminded of this is that one of the big theorems of the course is the simplicity of A5. I vaguely remember that NSB provided the icosahedron-based proof that's mentioned in the linked article, whereas IL provided a more intuitive and sensible proof.
One of the perks of being the official lecturer is that you set the exam questions. Imagine our delight when we opened the paper and saw the question: "By considering the rotations of an icosahedron, prove that the group A5 is simple"!