Risperidone – IMPURITY I – 3-[2-(4-{4-Fluoro-2-[4-(6-fluoro-benzo[d]isoxazol-3-yl)-piperidin-1-yl]-benzoyl}-piperidin-1-yl)-ethyl]-2-methyl-6,7,8,9-tetrahydro-pyrido[1,2-a]pyrimidin-4-one