code: func decomposeForSymMerge(length int,
  	comparators Comparators) (v1 Comparators,
  	w Comparators, v2 Comparators) {
  
  	if length >= len(comparators) {
  		panic(`INCORRECT PARAMS FOR SYM MERGE.`)
  	}
  
  	overhang := (len(comparators) - length) / 2
  	v1 = comparators[:overhang]
  	w = comparators[overhang : overhang+length]
  	v2 = comparators[overhang+length:]
  	return
  }
docs: // decomposeForSymMerge pulls an active site out of the list
  // of length in size.  W becomes the active site for future sym
  // merges and v1, v2 are decomposed and split among the other
  // list to be merged and w.