Copenhagen convention
When playing Copenhagen convention, after an opposing one-level opening, the three overcalls mentionned denote the three possible two-suited hands (5-5) in the suits excluding the open suit :
- 2NT : shows the two lowest-ranking unbid suits
- 3 ♣ : shows the two hightest-ranking unbid suits
- 3 CA: shows the top and the bottom-ranking unbid suit
Bids at the two level (barring 2 NT) are naturals.