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This is clearly not the same thing. Other than both of them adding additional dimensions to chess they have nothing in common.

that has 32 pieces this one has 20 not to mention that the peice setup and how the pieces travel across dimensions is totally different.

Do humans have to search all 10000 4d-chess ideas before LLMs to find the exact one that was plagiarized?

If you want to accuse it of plagiarism then yes (or have an LLM do it for you I guess)