How does Cas work and why can’t Man City appeal to it?

Jonty ColmanBBC Sport journalist and Katharine SharpeBBC Sport senior journalistManchester City’s Premier League charges, the Africa Cup of Nations winner being overturned, and contested athlete bans at the summer and Winter Olympics – all very different sporting controversies overseen by different governing bodies, but all linked by one organisation: the Court of Arbitration for Sport (Cas).