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Yuna Kim as the scores were read out.
The letter won't automatically trigger an investigation, and any protest at this stage is probably meaningless because rules stipulate that protests must be filed within 30 minutes of the event.
There's also some confusion about the status of the letter.
An IOC spokesperson confirmed to the Sydney Morning Herald that a protest letter had been sent, but the International Skating Union, which would handle any formal protest, told the AP that it had yet to receive the letter.
Nevertheless, it appears that South Korea is taking action as the country remains in an uproar over Russia's Adelina Sotnikova winning gold over the favored Yuna Kim.
More than 1.7 million people, 90% of whom were Korean, signed a Change.org petition to investigate the result.
Kim was the heavy favorite going into the event and skated cleanly. Sotnikova, who had never won a major international event before the Olympics, matched Kim's artistic score and beat her handily in the technical area.
The ISU came under fire after the event. One of the judges on the panel was once banned from the sport for trying to fix the 1998 Olympics. Another was the wife of the director of the Russian figure skating federation.