Non-deterministic loops

[fbatista]

From the IPG:

It is also slow play if a player continues to execute a loop without being able to provide an exact number of iterations and the expected resulting game state.

From the Annotated IPG:

This is one of those sentences that whole articles can be written about. Most loops have a finite ending — I do X 10 times, but stop early if Y happens. Using the rules for shortcuts as found in the MTR, you must also be able to explain the specific end state. There are many loops out there where they will reach a certain condition “eventually.” Eventually is not a specific number. These loop end states are also not specific enough. You cannot perform the loop “Mill myself until the last 2 cards in my library are Emrakul” because you can’t specify how many times you will need to loop to get to that state. You could loop “A million times!” but there is still a chance it won’t happen until the million and first. Fine, I loop 2 Million times! There is still the chance it won’t happen. It doesn’t matter how small the chance of failure is; if it’s there, you can’t loop. Also, if the opponent wants to respond when you have milled both Emrakuls and both shuffle triggers are on the stack, how do you determine which state happens first?

I highlighted the relevant bits that clash with our current "custom" policy of allowing non-deterministic loops.

We currently allow:

• Player A defines a stop condition for a non-deterministic loop.
• Player B defines a stop condition to interact with a non-deterministic loop.

But the problem is: How can we tell which event occurs first? Player A's or Player B's ?

Sometimes it's simple to figure out, but sometimes it's not. In the shuffle example above, it's definitely not simple, and requires going through the iterations one at a time.

With this in mind, it's OK to allow shortcutting for a non-deterministic loop, as long as no opponent wants to interact, however as long as one or more opponents want to interact, the judge will need to make a decision on allowing the shortcutting, and if the shortcutting is not allowed, because of a situation similar to the one described above, that means the loop will still be subject to potential slow play warnings.

[purplejudge]

This is an old issue and one that I'm not sure we can solve. If we draw the line "an opponent must want to respond", all they have to do is say they might want to, and the loop is now a non-loop. If we police it by saying "Well, what will you ACTUALLY do?", then it becomes important for the judge to know how all the decks involved play and consider strategy, which is not something we want to assume.

I feel like the best solution would be to follow the original MTR and not allow it in general. The reasoning is sound and still applies.

Since this would mean the end for a multitude of decks, I don't dislike the proposed strategy of "Is there a chance anyone might want to do something?", even if it is a glass canon. If the player can show the judge that they can perform any action (even if it doesn't relate to breaking the "loop"), then the looping player must perform all the actions. This also rewards players who study policy documents, which is a good thing

[fbatista]

Since this would mean the end for a multitude of decks,

I don't think this is true.

At most, only specific lines within a small number of decks will be affected (like the new atla palani deck lines with a +1 counter on it + shuffle titans + infinite mirror entity activations for 0 on the stack; or the gitrog cleanup sculpt).

In these, the judge will need to recognize an undeclared / unproposed loop and issue the slow play warning.

I also agree that we can allow for some leeway, by doing what we proposed: Allow the loop if everyone is ok with it. I know it's depositing too much faith in a player that is about to lose the game, and in many situations they will say they aren't ok with the loop, and they would need to explain why not.

[fbatista]

I think the solution here is to remove the non-deterministic loop policy from the cEDH PT League document.

Then we add an entry on loops saying:

---

Non-deterministic loops are allowed if and only if all opponents still playing agree to it. By default, Judges will not allow non-deterministic loops since it's not possible for opponents to specify a point in the loop to interact with, in a way that you can shortcut to and have a clear idea of what the game state looks like.