Algorithm

  Read observation source list
  Sort into order of descending count rate

  Read names of exposure lists used to create observation list
     from keywords in observation list
  Check that supplied exposure list was used to create observation list

  Read exposure source list
  Find index into ML_ID_SRC vector columns for the given exposure list

  while (source count rate > threshold && selected sources < maximum)
     Check nearest neighbour threshold

     Locate source in exposure source list

     Check source counts against threshold
     Check source count rate against threshold

     Add source to selected list if all checks passed

  end while

  Write selected list

The correspondence between sources in the observation source list and the detections in the exposure list is determined as follows:

• The observation source list contains a set of keywords M1_SET1, M1_SET2, M1_SETn, ..., M2_SET1, M2_SET2, ..., defining the names of the exposure lists which were used to create it.
• The observation source list contains columns M1_ML_ID_SRC, M2_ML_ID_SRC and PN_ML_ID_SRC which are vector columns. The nth element of the vector defines the value of ML_ID_SRC in the nth for the detection of that source in the exposure list for that instrument.