Leisurely browsing wikipedia and reading about trace diagrams I encountered the sentence
Several results in linear algebra, such as Cramer's Rule and the Cayley–Hamilton theorem, have simple diagrammatic proofs. They are closely related to Penrose's graphical notation.
but I didn't find any references or examples of these. Out of curiosity, how would such a proof look like? Is there a book or resource online for this?
A related and also unanswered question can be found at Two basic examples of trace diagrams?