For the time being I conclude then, that 1.c4 e6 2.Nf3 d5 3.b3 and 4.g3 avoids the Neo-Catalan Accepted without further objection. Interested readers should keep in mind to leave the bishop on c1 for a while.

Well, 3 g3 dxc4 is a different system, of course. If White wants this Neo-Catalan stuff then he has to go 3 b3 to take back with the pawn.

Actually Petrosian-Korchnoi was a bit different, the point there being that Black could go d4 at a time when he could still play ...f6 to support his centre. Although even then there used to be a system against the Saemisch involving ...b6 and ...c5, didn't there? Maybe not ...Bb7; in fact I think that what did for the system in the end was some e5/Be4 breakthrough.

Obviously if Black's going to play ...d4 and go into a reversed Modern Benoni White would like the bishop on c1, but maybe there isn't any concrete difference. Say it goes 3 b3 Nf6 4 g3 c5 5 Bg2 Nc6 6 00 Be7. White's target position would arise after 7 Bb2 00 8 e3, as in various games Miles-Geller and others. Should he go 7 e3 first then 7...00 8 Bb2, I wonder? Say he goes 7 Bb2 d4 8 e3; can Black get away with 8...e5?

I'm not sure. You might be right and it makes no real difference, but I'm pretty sure Watson says in the book I mentioned above that it's more accurate to dealy Bb2. I might have misremembered or it might just be a matter of cutting down Black's options, because I don't recall e3 coming before Bb2. I'll have a look tonight and see if I can offer any vicarious enlightenment.

MNb, in your sequence is 4 Bb2 not a well-known mistake along the lines of Petrosian-Korchnoi, candidates 1971 (although a slightly different position), and White ought to get to it with g3?

I don't see 3....d4's anything to worry about. Black's going to have to play ....e6-e5, so White just gets a Benoni/Yugoslav with his extra tempo plus the tempo b3, which may come in handy or it may not.

You could try heading for a Catalan after 2.Nf3 and 3.g3.  Don't forget that Black may also play 2...f5 with a Dutch.

I agree with you. Most Black players hate this stuff. Botvinnik and Miles did well with it, among others. John Watson's English IV, back in 1066 or so, had a very good chapter on it, but I don't know of anything more recent. Botvinnik-Larsen, Monaco 1967, was a White model.