Claiming that petitioner had breached its contract to pay $150,000 for the exclusive use of the trademark "DAIRY QUEEN" in certain portions of Pennsylvania, the owners of the trademark sued in a Federal District Court for (1) temporary and permanent injunctions to restrain petitioner from any future use of or dealing in the franchise and trademark, (2) an accounting to determine the exact amount of money owing by petitioner and a judgment for that amount, and (3) an injunction pending accounting to prevent petitioner from collecting any money from "Dairy Queen" stores in the territory. Petitioner filed an answer raising a number of defenses and made a timely demand for a trial by jury. The District Court struck petitioners demand for a trial by jury, on the alternative grounds that either the action was "purely equitable" or that whatever legal issues were raised were "incidental" to equitable issues. The Court of Appeals denied petitioners application for a writ of mandamus to compel the District Judge to vacate his order. Held: The District Judge erred in refusing petitione