I am trying to grok the fide specification of the swiss pairing algorithm, having a hard time with that. For example rule A.4.b reads:
After two players with different scores have played each other in a round, the higher ranked
player receives a downfloat, the lower one an upfloat.
According to definition A.2 the player rank changes dynamically, round after round. My main question here is, at what time the rank of the two players is considered, before or after the round? I personally see arguments for both interpretations.
If I understand correctly, swiss system tries very hard, not to pair moved down players against each other, this is only considered if all other possibilities are exhausted. Hence if a player was moved down because of rule A.4.b or for some other reason he will be likely paired against a player with different score which is lower ranked before the game and subsequently be eligible for another application of rule A.4.b, either unconditionally or if he stays on top of this opponent. Hence because of rule A.4.b I expect downfloats to be positively correlated, which seems to contradict the main pairing construction.
It would be helpful if someone with experience in this matters, could either confirm or correct this interpretation and provide some intuition, for what rule A.4.b was introduced for.