Leinster are one of three teams through to the quarter-finals, but are not yet assured of a home tie. To join them Munster would need to beat Gloucester and most probably score five tries more than the opposition at Thomond Park on Saturday, while Ulster need to beat Northampton in Ravenhill and in the process score four tries more than their opponents.

Once again the permutations are endless and mindboggling as the final series of pool games approaches next weekend.

That is always liable to be the case when the six pool winners are joined by the two best losers, with the top four ranked pool winners earning home advantage in the quarter-finals. As things stand, Toulouse, Leinster and Leicester are all through to the last eight. None are yet certain of a home advantage.

In Leinster's case their task away to Bristol next Sunday has been made more complex by their opponents having beaten an under-strength Montferrand in France yesterday 30-22. Theoretically, this keeps Bristol in the hunt as one of the two best runners-up.

Presuming Leinster win and secure the second best ranking, they would most likely play the best placed runners-up, who will probably come from Pool Two thanks to the 47 tries Viadana have leaked so far. Alas, it's far more likely to be Gloucester or Perpignan than Munster.

Gloucester can win the pool by drawing or becoming the first away side to win at Thomond Park in the competition's history, while Munster must win to have any hope, but even then the best they can hope for is a three-way tie unless Perpignan don't win in Viadana.

In the event of a three-way tie, rules decree only the six matches involving those three sides will be used to determine the standings.

The first criteria would be the greater number of match points, which would be four each between Gloucester, Perpignan and Munster, after which comes the tally of tries in those six matches, and if level still the points difference in those relevant games.

Perpignan have 11 tries from those games, while thus far Gloucester have nine and Munster five. Furthermore, while Perpignan's points difference against their main rivals is -3, Gloucester's is +28 and Munster's is -25. Hence, a win and outscoring Gloucester by three tries will not be sufficient for Munster.

Even scoring four tries more than them would not suffice unless Munster's winning margin was 27 points or more. Alternatively, they could mathematically overtake Gloucester by winning and outscoring them by five tries.

So there is the stark task for Munster - win by four tries and a margin of at least 27 points, or by five tries.

Munster will also be mindful of the Irish seedings for next year. Miffed that they were seeded second behind Leinster, they wouldn't want to be relegated to third behind Ulster next season.

Given their injuries and the competitiveness of their pool Ulster have done well to be in with a chance of winning Pool Six, though win they most probably must against Northampton as their try tally of seven so far gives them little hope of qualifying as one of the best losers.

Ulster must win to have a hope, and most probably that would also lead to a three-way tie unless Biarritz slip up at home to pointless Cardiff. In such a scenario, again it would come down to the tries scored and then the points differences in the six matches involving the three pool leaders.

Northampton have scored six tries in the relevant matches to three apiece by Biarritz and Ulster, while Northampton's points difference is +23 and Ulster's is -24.

So Ulster need to beat Northampton and score three tries more, while winning by at least 24 points, or else win and score four tries more than Northampton.