Lawvere's fixed point theorem as a generalisation of Cantor's theorem is a big result. https://ncatlab.org/nlab/show/Lawvere's+fixed+point+theorem https://ncat

Lawvere's fixed point theorem as a generalisation of Cantor's theorem is a big result. https://ncatlab.org/nlab/show/Lawvere's+fixed+point+theorem https://ncatlab.org/nlab/show/Lawvere's+fixed+point+theorem Emily Riehl: "The author is told with distressing regularity that 'there are no theorems in category theory' ... Sadly, the majority of the theorems that are personal favorites of the author were excluded because their significance is more difficult to explain." (long list of theorems) https://math.jhu.edu/~eriehl/161/context.pdf https://math.jhu.edu/~eriehl/161/context.pdf