Roger Federer and Elmo from Sesame Street seem to disagree on the letters of the alphabet in a Super Bowl ad for ON running shoes.

Watch as Elmo sits in an umpire's chair and debates the two letters found on Federer's On-branded sneakers: Is it 'Q' and 'C' or 'O' and 'N'?

Elmo has been around a long, long time, and he's one of the few characters that all of the generations that have come forth since the 90s know and love.