Notes for AKT-090910-1/0:26:16

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Invariance of tricolourability under R1. There are 2 directions to check, i.e. (left) 3-colourable [math]\displaystyle{ \Rightarrow }[/math] (right) 3-colourable, and (left) colourable [math]\displaystyle{ \Leftarrow }[/math] (right) colourable. Side benefit: explanation of 'local' diagram notation.