History
Constitutional Courts and Federal-Provincial Jurisdictional Disputes
Quick fact
In Canada, the Supreme Court has used the 'pith and substance' doctrine to strike down provincial laws that encroach on federal powers—like when a provincial law attempted to regulate aeronautics, which is a federal responsibility.
Why this is interesting
Who settles the fight when a province and the national government both claim the right to make a law? In most countries, it's not a politician—it's a panel of judges.