Hey, I don’t agree with the above advice you’ve been given.. I think it’s great to mention your hobbies, especially when they are linked to mathematics (and I was an A Level maths student while being a member of the senior girls choir so I can appreciate the correlation). Definitely mention the guitar but the names and creators of the song are irrelevant and don’t need to be mentioned.. I’d leave it out just in case it causes problems.. Maybe if you have an interview you could talk further about the music you play and composers etc