Bell inequality for qubits based on the Cauchy-Schwarz inequality
  We develop a systematic approach to establish Bell inequalities for qubits based on the Cauchy-Schwarz inequality. We also use the concept of distinct "roots" of Bell function to classify some well-known Bell inequalities for qubits. As applications of the approach, we present three new and tight Bell inequalities for four and three qubits, respectively. 
Jing-Ling Chen and Dong-Ling Deng