         
                                                                           CH＝C－CH
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                                                                                                                                                                  CH             
                                                                                                                                                                
                                                                           A  B           
  —A—B—A—B—A—B—A—B—A—B—A—B—A—B—A—B—
  —A—A—A—B—B—A—A—A—B—B—A—A—A—B—B—
   —A—A—A—A—A—A—A—A—A—A—A—A—A—A—A—
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                                                 B                      B                  B                       B                         B
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                                                 B                     B                  B                        B                        B
   —A—B—B—A—A—A—B—A—B—B—A—A—A—B—A—B—
                                                                
       —                                        10—16                                    10—16                                     