DavidKok, on 2021-May-30, 06:20, said:
Here in the Netherlands Dutch Doubleton is very popular, but I think the degree to which it is non natural and the degree to which it is suitable for beginners are inversely related. I do not think it matches the requirements of the original post.
I could talk about Dutch Doubleton for days without pausing for breath, but at its core there are three different systems called 'Dutch Doubleton'. One is basically SAYC except that 4=4=3=2 shape and points outside your 1NT/2NT opening range you open 1♣, instead of 1♦ (this way 1♦ always promises 4). In my opinion this is not noticeably better or worse than SAYC, and it would be a stretch to call this an unnatural system (although 1♣ needs to be alerted).
A step up is described in the previous link to Rosalind's website (although the 2NT weak minors is not standard, most people here play 20-21 or 20-22 NT). In this version of Dutch Doubleton you open 1♦ only with 5+ or exactly 4=4=4=1. This means that a whole host of hands with 4 diamonds and 2 clubs will be opened with 1♣. Normally people add a 'relay' 1♦ response to 1♣, showing either real diamonds (often in conjuction with Walsh principles, so it denies a major unless GF) or any 0-7 HCP hand without long clubs. Opener rebids their longest major with a weak balanced hand (can be only 3 and needs to be alerted) or 1NT with a hand too strong for a 1NT opening (usually 18-19). This caters to the increased frequency of opening 1♣ on only 2, so you can run to a major suit. The 1♣ opening and 1♦ response need to be alerted.
I could talk about Dutch Doubleton for days without pausing for breath, but at its core there are three different systems called 'Dutch Doubleton'. One is basically SAYC except that 4=4=3=2 shape and points outside your 1NT/2NT opening range you open 1♣, instead of 1♦ (this way 1♦ always promises 4). In my opinion this is not noticeably better or worse than SAYC, and it would be a stretch to call this an unnatural system (although 1♣ needs to be alerted).
A step up is described in the previous link to Rosalind's website (although the 2NT weak minors is not standard, most people here play 20-21 or 20-22 NT). In this version of Dutch Doubleton you open 1♦ only with 5+ or exactly 4=4=4=1. This means that a whole host of hands with 4 diamonds and 2 clubs will be opened with 1♣. Normally people add a 'relay' 1♦ response to 1♣, showing either real diamonds (often in conjuction with Walsh principles, so it denies a major unless GF) or any 0-7 HCP hand without long clubs. Opener rebids their longest major with a weak balanced hand (can be only 3 and needs to be alerted) or 1NT with a hand too strong for a 1NT opening (usually 18-19). This caters to the increased frequency of opening 1♣ on only 2, so you can run to a major suit. The 1♣ opening and 1♦ response need to be alerted.
Nothing unusual in most of Europe about opening 4=4=3=2 as 1♣, which they will play as standard once they move to Italian 2/1 anyway.
I can live with the rest (after reverting to a normal 2NT) but as you say it's more a variant of the target system than a simple alternative.