I've been thinking about a (strong) notrump defense that is legal under the ACBL general chart that has immediate natural 2M and 2♣ for the majors while differentiating relative lengths of major/minor two-suiters. Here's what I've come up with; feel free to tear it apart. I have no idea if this is defense already exists. (1NT) strong -X minor single-suiter or hearts and a minor, at least 5-4 either way -2♣ majors -2♦ spades and a minor, at least 5-4 either way -2M natural -2NT minors Over 2♦, advancer bids 2♥ to ask overcaller about spade length. He rebids: 2♠ 5 spades, 4+ minor 2NT 4 spades, 5+ clubs 3♣ 4 spades, 5+ diamonds (These are just steps, 3m could be natural and 2NT could be something else, maybe a stronger hand if that makes more sense.) This way advancer can play in a 5-3 spade fit when it exists and 3m when it doesn't. It's obviously very vulnerable to disruption by responder, and a downside is that it lets responder bid 2♥. Over X, advancer bids 2♣ is pass or correct (to 2♥ with hearts and a minor) and 2♦ to ask for more information. Then, 2♥ 5 hearts, 4+ minor 2♠ 4 hearts, 5+ clubs 2NT 4 hearts, 5+ diamonds 3m natural, 6+