Conventional treatment of a particular negative double
As I understand things these methods originated in Italy. Many Italian experts play that the double shows 4 or 5 spades and hands with 6+ spades start with 2H. I've tried this in a few partnerships but don't yet have enough experience with it to say how well it works. The partnership does need to agree on followups over 2H since it has a wide range - most use 2N as an artificial ask.