The Chinese government issued a ban on the letter after people were using it in online posts to criticize current president Xi Jinping’s plans to rule the country indefinitely, reports Business Insider. In China, the letter N is used to represent unknown numerical values in math formulas (as the letter X is used in the States). The government issued the temporary online ban on the letter after posts began appearing in joke equations that claimed to mathematically describe the president’s length of rule (such as “N = infinity”). The ban apparently lasted only a day, however, as by Tuesday morning, Chinese users found they could use the letter in online posts and text messages once again.