[(A ^ B) ^ C]1      
                                  ---------------        
      [(A ^ B) ^ C]1                    A ^ B               [(A ^ B) ^ C]1
    -----------------                 --------             ---------------
          A ^ B                           B                        C
         ---------                     ----------------------------------
             A                                          B^C
       -----------------------------------------------------------
                                         A ^ (B ^ C)
                                 ------------------------------ (1)
                                       (A^B)^C --> A^(B^C)