[FrancesHinden]

I think you can tell from the answers here that there isn't a standard way of playing this.
I'm assuming that 1NT didn't deny 4 spades (in spite of Two4bridge saying it does, most people play that it doesn't)

One possible agreement is that going through checkback always promises 5 cards in your major. That's an easy rule, and leads you to deduce that:

1D-1H; 1NT - 2C; 2D - 2S is 4-5 in the majors, at least invitational; while
1D- 1H; 1NT-2S is 4-4 in the majors, at least invitational

Not playing 2-way checkback, you need to play both of these as forcing.

You can then think about 1D-1H-1NT-2C-2D-2H. There are three ways to play this, all of which work:
(i) invitational with 4-5 majors, NF (why did you bother with 2C if you didn't have 5 hearts?) then 4S is 4-5 majors FG
(ii) a light invite with 5 hearts (a strong invite bits 2C-2D-2NT which implies 5 hearts by the above agreement)
(iii) a weak hand with 4 spades and 5 hearts. Solves the problem of missing a 4-4 spade fit.

[mike777]

Frances raises the interesting point that 1nt does not deny 4s here very often at the expert level.


1d=1h
1nt?


this is very different from say:


1c=1d
1nt? where it is very common to not bid a 4 card major.