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Physically, each ETS node will introduce a thread. Thus, the intersection operator must synchronize the upstream input threads in order to generate the correct result. In order to have a pipeline operation, the intersection is implemented in a sort-merge manner. Therefore, each input is required to be sorted. The synchronization is handled by the thread of input No.0, which means the thread 0 will call the writer.open/nextFrame/close functions. If we authorize arbitrary threads to push forward, the downstream operator will be confused, especially in synchronizing their locks. The core logical intersection function is as below:

1. do 
   1. find the max input: maxinput id of the maximum record
   2. for each input i
      1. if record < max keep popping 
      2. if record == max keep popping until it matches max. then match++; continue
      3. if > max, break
   3. If match == inputArity
      1. output max record
2. while no input is closed.

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