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Kaplan Inversion/Granville

Back in the mid-90s, my primary partner at the time said something like "Oh hey we should switch the meanings of the 1 and 1NT responses to a 1 openings" and I said "OK cool" and we did literally/simply that: 1-1 denies 4 spades and 1-1NT promises 4+ spades (let's call this KI4) and making only the obvious corresponding changes to the followups.

Then starting in the late 90s I took a bridge hatus of ~6 years during which time the KI dropped off the GCC, and since this partner now lived on the opposite coast and I was mostly playing in GCC environments, I didn't give it much more thought.

However in the last couple years, we've made concerted efforts to try to play in at least one NABC per year together, and I've also had some success in goading other partners into adopting this in mid-chart events.

Somehow, it wasn't until this year's Wernher that I encountered enough other KI players seated the other way to realize that most of them (it seems) play 1-1 as 0-4 spades and 1-1NT as 5+ spades (let's call this KI5).  IIRC there was at least one other pair playing KI4 though, but maybe they're poor confused souls like me.

Most of the Google hits imply KI5 as well.  Does 1-1-1NT always promise 4 spades then?  Does it specifically promise 4=5=2=2?

Does anyone consider KI4 a playable alternative?  As you can see, I haven't given this a tremendous amount of thought; but it would seem like opener gets to rebid 1NT more often on any (semi-)balanced hand with fewer than 4 spades and without giving up as much shape info (I suppose conversely in KI5 responder bids 1NT more frequently but it also feels like this effect would be smaller)

For my purposes/interests the system context would be

  • limited openers (1M 11-15 in a strong 1 system or 1M 11-17 in a strong 1 system as currently played)
  • weak NT, open 1NT frequently with 5-card major (opening 1M implies distribution or else a sound balanced hand)
  • although I play variable NT (14-16 in some cases) with one partner
  • FWIW none of my partnerships currently use Gazilli

Maybe in 11-15 your range is so narrow you don't care as much about 4=5 and reverse more freely so you don't need KI at all?

Maybe in a weak NT context as described above a lot of the hands that would rebid 1-1-1NT in KI4 have already been opened a weak 1NT, which is an argument for KI5?  (although in the variable NT case I'd prefer it if our 1M response structures were consistent regardless of what a 1NT opening would have meant...)

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