Leading article: A new smile that keeps an old secret The discovery of a picture, believed to be the earliest copy of the Mona Lisa, has prompted a discussion about whether the existence of a contemporary copy might in some way devalue the original. Is one Mona Lisa worth more or less if there are two, and what if there were more? If the two were identical in every detail, then it could be argued that the "original" had lost some of its cachet; there could even be a vituperative artistic row about which - the Louvre's or the Prado's - came first. But they are not identical. The chief value of the copy, so the experts say, resides in its better condition, which leaves - perhaps - a more faithful impression of the sitter. The more remarkable truth, however, is that the presumed pupil captures the same enigmatic smile as did the master. The mystery is thus deepened, rather than explained. No value, monetary or otherwise, is lost or gained; the real Mona Lisa keeps her secret.