The phrase "are corner" doesn't have a single antonym. However, if we look at the two words individually, we can come up with some antonyms. "Are" means "exist" or "occur", and its antonyms could be "don't exist" or "do not occur". "Corner" means a sharp edge or a turn, and its antonyms could be "straight" or "curveless". Putting these two antonyms together, we could say that the antonyms for "are corner" could be "do not exist straight" or "straight without a curve". However, it's important to remember that these phrases are not commonly used and may not make sense in all contexts.