HERE at Keeping Posted we've always felt that science was something best left to scientists. But that was before we came upon Professor Lotfi Zadeh, who gave the world the concept of fuzzy logic, a term now part of everyday phraseology. A Russian of Iranian descent (which isn't as illogical as it may sound), he tells us with disarming candour that fuzzy logic - basically science in an informal and people-friendly form - was born out of an argument he once had with some friends as to whose wife was more beautiful. Professor Zadeh, who will be expounding his theory at the Chinese University this afternoon, adds: ''Beauty is, of course, rather difficult to determine objectively.'' We know exactly what the learned academic means, especially after hearing of a thief who broke into the bedroom of a well-known socialite. Apparently all he took was one look!