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{{1,0,0,0},{0,1,0,0},{0,0,1,0},{0,0,0,e^{i(pi)}}}.{{15,9,5,-3},{9,15,3,-5},{5,3,15,-9},{-3,-5,-9,15}}.{{1,0,0,0},{0,1,0,0},{0,0,1,0},{0,0,0,e^{i(pi)}}}