[Kungsgeten]

I do not know if this idea of a gadget has been discussed before, so I present it here. I got the idea while reading this article of the Lisa convention and these system notes by Fallenius and Welland. So what's the deal?

When playing a forcing or semi-forcing 1NT response opener may rebid 3-card minors and responder may have invitational values (or even better if playing forcing 1NT) or weak values. The treatment presented here allows responder to invite with less than 4, exactly 4, or 5+ diamonds. He may also sign off or invite with 6+ clubs.

1H--1NT; 2D---
Pass = Preference
2H = Preference
2S = Artificial. Weak with 6+ clubs or invitational with exactly 4 diamonds
2NT = Invitational, less than 4 diamonds
3C = Invitational, 6+ clubs
3D = Invitational, 5+ diamonds
3H = Three card limit raise

After responder's 2S rebid opener can bid 2NT or 3C:

1H--1N; 2D--2S;
2NT = Will not accept the invitation. Normally 3 diamonds, but may be 4 diamonds which prefers to play NT
3C = Either 4+ diamonds or 3+ diamonds and a hand which will accept the invitation.

Now responder bid pretty natural. He may pass, bid 3C over 2NT (to play), bid 3D (invitational over 3C) or bid 3H (three card limit raise with good diamond support).

[whereagles]

Neat idea. It's advanced stuff, but seems sound.

[Zelandakh]

What are you bidding with a hand with diamond preference and less than invitational values that nonetheless wants to play gane opposite a maximum opening? The usual structure allows for 2 ranges of diamond raise here - this is what you have lost in order to show 4 versus 5 card support.

[yunling]

No problem if 1♥-1NT-2♦ is limited.
But playing standard, agree with Zel that you need 2♠&3♦ for 2 ranges of ♦ raise here, something like 8-10/11-12.