You found Mr. Klein!
Mr. Klein is the ghost of Felix Klein - a German mathematician, who described the so called Klein bottle. That is a one-sided, non-orientable surface, which is formed by attaching two Mobius strips to each other along their boundaries. Being an apparition himself, Mr. Klein enjoys showing up around various optical illusions, preferably impossible objects. His favorite ones are the Penrose triangle and the Penrose cube - famous illusions created by Oscar Reutersvärd.
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