Compactness does not mean density it means small size and need not be dense
Opacity does not mean density - in photography it refers to how much something can block light from passing through it. In photoshop they use density for masks to define a combination of opacity ( for black ) and transparency ( for white )

I’ve still no idea what the Jaja set refers to the explanation left me non the wiser

I🤔🤔🤔

@Neil. I think you're being over-picky about compactness, TBH, it's close enough. The Jaja set is eggs, although it should be Roe, not Rhos.

Overall not too bad but certainly could do with better explanations.