With my regular partners, I play 1♥/
♠ - 2NT sequence as four (or more) card fit and invitational or better values. I know for North Americans this shows game forcing values with fit 4+ (Jacoby 2NT), but in Europe "fit 4+, INV+" is more popular and I think it's better.
There are many ways to continue after such a start. For some years, I was quite happy with the simplest system: the rebid of the opened major, from both sides is minimal and can be passed; anything else is (semi)natural, in first instance a game trial bid, but can reveal later a slam tentative.
One of my partners insisted this is too rudimentary and proposed a very complicated scheme, but I'm a simple soul and resisted ;-) I'll probably detail that later, but for now i want to propose my original(?) and simple scheme, which is based on losing trick count (LTC). I found this to be very appropriate, since we know about a nine card fit, LTC should be adequate.
So, after 1M-2NT, the opener bids his loser count in steps:
- 3♣ = minimal hand (7 losers or worse).
- 3♦ = 6 losers
- 3♥ = 5 losers
- 3
♠ = 4 losers or better (but with 3 losers you probably open 2C)
Higher announces are still to be refined, for now I propose: 4♣/♦ = 5-5 hand, non-minimum; 3NT = not defined yet (specific Ace ask it's an option).
After the 3♣ = minimal hand, the responder can
- use 3♦ as a general game essay
- try to sign off in 3M (opener may override and still bid game)
- blast the game
- bid anything else with slam interest (cue-bid)
After 3
♠ (4 losers), you are for sure in slam zone and will continue with cue-bids. A grand is not excluded ;-)
After the other step responses, the responder can see at a glance if there is slam possibility by counting his potential cover cards and continue with cue-bids or stop in the game.
It would be only fair to add that I don't insist this is the best system over 2NT "fit 4, INV+". It's just an untested idea, which appeals to me because of the simplicity and apparent efficacy. Your mileage may vary.
References on losing trick count (LTC):
-
wikipedia on hand evaluation methods-
bridgeguys glossary-
Ron Klinger's book on AmazonLabels: bidding conventions