The Supreme Court justices had a lively discussion yesterday during arguments in King v. Burwell about who Congress intended to get health insurance subsidies and under what conditions.

The central question is whether the Internal Revenue Service had the authority to write a rule authorizing subsidies to go to millions of people in the 37 states now operating under federal exchanges.

The plaintiffs say the language of the law is clear: Subsidies are allowed in “an Exchange established by the State under [section] 1311of the Patient Protection and Affordable Care Act.” It doesn’t just say this once, but nine times in various linguistic forms.

The government argues that it is just a typo in legislative drafting: Congress clearly wanted subsidies to be available to citizens of all of the states, and the IRS therefore had the authority to write its rule authorizing subsidies in both federal and state exchanges.