From: Paul Vinkenoog <paul@vi...>  20070102 23:02:15

Hi Mimmo, >> So whether you interpret NOT IN() as NOT( IN() ), or as a >> conjunction of inequality tests, the outcome is the same. > You're right. My fault: I switched my notes. > Anyway it's interesting: "my" interpretation of NOT IN() is > equivalent, only if De Morgan "rules" and other principles of > classic logic remain valid in NULLable logic. Yes. I guess they do because with NULL added, the symmetry is preserved: not(null) == null, and most other operations return null. The only exceptions are "null and false" and "null or true", and there's symmetry there too. You can also prove either one from the other: null and false == false <=> not(null and false) == not(false) <=> not(null) or not(false) == true <=> null or true == true OK, I cheated: I used De Morgan in this "proof" ;) The proper thing to do is work out the truth tables, but that's boring. Greetings, Paul Vinkenoog 