3NT -

8 to 9 playing tricks

7+ card M with 1,5 LT max

4♣   =    transfer to your M

4♦    =    bid your M

4♥♠    = SI with singleton or void in ♥♠. OP can continue with 1 LT or less in his M. If  she holds oM, she must bid 6 oM

In competition

pass = forcing below 4 of 'our' major

other = nat