Comparable Calls
I find it reasonably easy to judge if a replacement call is comparable however, I seem to get confused trying to find a subset call.
I would like to ask if any person could explain in more detail what would be a subset for a comparable call. Maybe a few examples because I am out of my depth if called upon to explain a subset to players.
Comments
I wouldn't use the word "subset" to players unless you know they are of a mathematical/logical bent.
In a bridge context I think a good way to explain is "you can make any call as long as partner hasn't learned anything only because of the infraction" * because that gets to the reason for the law.
(*That is, the information given by the comparable call is a subset of that given by the original call)
The WBF tells us to be generous in our interpretation, so perhaps it's better to say "you must not give partner any significant/substantial information they don't deserve"
For natural bids, an alternative way to look at it is to say "(virtually) Every hand that makes the new (comparable) call must also have made the original (disallowed) call." (That doesn't always work for artificial bids)
Scenario 1: You open 1S in second seat, out of turn. It isn't accepted and your RHO opens 1D.
Now, a 1S overcall isn't a comparable call because (for example) it doesn't show opening bid values. So there are hands that overcall 1S that don't open 1S. Partner has learned more about your hand than he would have done without the disallowed 1S opening, and that might be useful (e.g. he has a marginal invite or penalty double).
A 1S overcall is NOT a subset of a 1S opening.
A 2S intermediate jump overcall is a comparable call, because every hand that overcalls 2S would open 1S (it shows opening bid values and it's more specific about length and range). Partner hasn't gained anything from the irregularity, so it's allowed.
A 2S intermediate jump overcall IS a subset of a 1S opening. {edited on Frances' behalf in line with her comment below}
Scenario 2: You play a multi, 2D showing a weak 2 in a major or an Acol 2 in a minor. You also play weak jump overcalls.
You open 2D in second seat out of turn. RHO doesn't accept and opens 1D.
You can overcall 2S as a weak jump, because that's more specific than the multi opening: partner hasn't learned anything from the disallowed multi.
However, if you have one of the strong options, you can't double. Now partner would know that you don't have a 'normal' take-out double, you must have a strong minor single-suiter. He only knows that because of the disallowed multi, so that's not allowed.
Scenario 3
Partner bids 4NT Blackwood. It took partner a long time to do that and you were idly thinking about the previous hand and whether you should have overcalled 2D. You respond to Blackwood with an insufficient 2D. This is completely meaningless. So you can replace it with anything you like, because partner hasn't learned anything from the insufficient call.
Just too late to edit the above.... I meant to say at the end of Scenario 1
A 2S intermediate jump overcall IS a subset of a 1S Opening
An easy way to think about subset calls: when replacing a call with a comparable call based on subset-of-meanings, the replacement call isn't allowed to give any less information, but is allowed to give more information. For example, say I open 1!s out of turn, and RHO rejects this and opens with 1NT. If my 1NT defence has a bid that specifically shows opening values, 5+ spades, and a 4+-card minor, I can make that bid without having to suffer the penalty for making an incomparable call; it gives all the information that my 1!s opening would (i.e. that I have opening values and spades), and it doesn't matter that it gives additional information as well (i.e. that I have a 4+-card minor).
Now suppose that my 1NT defence instead has a call that shows opening values, a 4+ spade suit, and 4+ cards in another suit (and I'm playing a 4-card majors system). This seems similar, but it doesn't convey all the same information that the 1!s opening does (if I open 1!s on only 4 spades, that denies holding a longer minor, whereas my defence to 1NT could have a minor that's longer than spades). So that call wouldn't be comparable; there's an important piece of information in the 1!s bid (the relative lengths of spades and the minors) that the replacement call wouldn't convey.
I fixed it for you.
I would be loath to disallow* a call that means "Spades and a minor that could be longer" when the disallowed call is "Spades and I might have a minor of the same length". I would treat it as a subset (even though it technically isn't) and be prepared to use 23C if needed. After all - a one card difference is not supposed to be regarded as significant.
Of course with all bridge being played online the need for Law 23 is somewhat diminished :)
*disallow = not regard the replacement call as comparable.
My experience with playing artificial defences to 1NT is that knowing the relative lengths of partner's major and minor is actually very useful information, at least at matchpoints (to the extent that the "Woolsey" defence, which is commonly played at the top level, has separate calls for longer major+shorter minor and for shorter major+longer minor). The only real downside of such a system is that you sometimes end up in the wrong suit when you have a double fit, due to not knowing the relative lengths. As such, it seems wrong to allow players to gain that information from an irregularity, when not having that information is the main downside of the system they're playing!
Of course, the withdrawn call should be UI, so advancer should intentionally aim for the wrong contract if it's a logical alternative. In practice, though, it'll be very hard to explain that particular subtlety to the players.
Am I alone in thinking that rulings were so much simpler and more easily accepted by players under the old laws? Personally, I had never heard the word "subset" before!
Re subset - on opening 1S bid is 4+ spades and say 10-20 points...
An intermediate jump overcall of 2S shows 11-15 points and 6+ spades.
11-15 and 6+ spades is a subset of 4+ spades and 10-20 points.
Therefore an intermediate jump overcall of 2S is a subset of 1S.
In addition, should a pair play opening strength Landy over 1NT, then the following is allowed...
? - 1S* out of turn and declined...
1NT - 2C* - landy showing 10-15 points and 5-5 in the majors...
Again this is a comparable call - the presumed opening bid of 1S shows 4+ spades and 10-20 points
The replacement bid shows 5+ spades and 5+ hearts and 10-15 points - this is completely and wholly confined within the the full set of possible hands that would have opened 1S. Which means that partner knows nothing more due to the bid out of turn.
As previously mentioned, the intent is to get to a sensible bridge result as often as possible, so the director can always be called back to make a judgment later on.
As an aside - I far prefer this new rule when compared to players making a total guess at the best final contract and getting a top or bottom on the back of the success or failure of that guess.
They led to more random results where a player had to punt the final contract.
" I had never heard the word "subset" before!"
If you don't find it helpful to use it, don't. It's only one way of explaining the law.
Many bridge players (and directors) have a mathematical/engineering or similar background and find the mathematical/logical language helpful. Others don't.
If I were giving a ruling, there are players where I would use the subset terminology and expect them to understand and find it a helpful explanation.
There are others where I'd use the alternative (suggested above) which is along the lines of "have you learned anything from the bid that isn't allowed that you wouldn't otherwise know?"
There are others where I'd not be generic at all, but have a chat with them away from the table and be very specific on what replacement calls I would allow and which I wouldn't, without trying to explain the Law in general.