In Reddit, especially on r/badX (like r/badmathematics or r/badlinguistics) subs, R4 is a comment placed after the post made by the same author to explain why the content linked by the post is bad, therefore it is suitable for that sub.
R4: Apparently OP believes that the operations you can do with a number based on how it was constructed. For example, they think that you can't "unsquare" 64 to get its square root if it was constucted by some manner other than squaring 8. At least as far as I can understand their post.
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