Risperidone Impurity: 3-[2-[4-(6-Fluoro-1,2-benzisoxazol-3-yl)-1-oxido-1-piperidinyl]ethyl]-6,7,8,9-tetrahydro-2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one(risperidone cis n-oxide).