Given the depth of bitterness that still exists over Japanese atrocities committed half a century ago, it is unlikely any act of atonement will ever be considered sufficient. Tokyo is expected to go further than before to bury this legacy when Prime Minister Keizo Obuchi apologises for his nation's wartime aggression during today's summit with President Jiang Zemin. However, the way the two governments continued wrangling over the wording of this apology, which is still likely to fall short of Beijing's expectations, almost until Mr Jiang's arrival yesterday, only illustrates how Sino-Japanese ties still remain more uneasy than those between most other major powers. Relations though have clearly improved. Mr Jiang's visit is the first by a Chinese head of state and, as such, of great symbolic value in protocol-conscious Tokyo. Economic ties are also of great importance. Despite the dismal state of the Japanese economy, Beijing remains by far the largest beneficiary of the nation's bilateral aid programme. Japan is also a valuable ally in China's fight to join the World Trade Organisation. But tensions remain and continue to erupt over new issues. The legacy of the past means Beijing remains understandably suspicious of Tokyo's involvement in any military matters. That has long manifested itself in China's dislike of the US-Japanese defence treaty, especially since the release of new security guidelines seen as enhancing Tokyo's role. The possibility that the defence of Taiwan may fall within the ambit of these guidelines poses another obstacle. Now Japan's enthusiasm for a missile defence system has created a further cause of discord. Not surprisingly, Tokyo feels it has serious security concerns following the recent firing of a North Korean rocket over its territory. But Beijing refuses to recognise this. Some of these differences may be glossed over in today's summit and amid the euphoria surrounding this ground-breaking visit. But they are unlikely to be resolved. Instead they serve as a reminder that, for historical and cultural reasons, Sino-Japanese ties are always going to be fraught with difficulties. Relations may now be better than at any time this century but the two countries are never destined to be close friends.