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I just noticed that the question What is the smallest number of 45∘−60∘−75∘triangles that a square can be divided into? posted by KGB_z recently, was posted on MSE in June by Ed Pegg. The titles are identical. Here is the MSE link. Since Ed Pegg has an MO account under his own name, presumably KGB_z is not Ed Pegg.
It is quite unlikely that they are the same person. The user in question has not provided a real name or contact info, but I believe the same person uses the name "kermit" at MSE.
The user behind KGB_z appears to have many accounts on MathOverflow. I don't see any evidence of abuse of the voting system, though, so this is fine. The plagiarism is unfortunate; I've closed the question, leaving a comment asking KGB_z to be careful about this in the future.
Often, when a question is posted by different people in different forums almost simultaneously, it means they both got it from the same source. But that does not seem to be the case here.
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