Can Gen John de Chastelain square the impossible circle on decommissioning? Increasingly the two governments, and political leaders in Northern Ireland who want the Belfast Agreement to work, are looking to this quiet-spoken Canadian to help them surmount the latest hurdle in the peace process.
They hope that he will be able to work out a formula which will persuade reasonable unionists that the republican movement as a whole is serious about meeting its commitment under the agreement to "the total disarmament of all paramilitary organisations", while at the same time meeting the requirements of the IRA and other groups that such a step should not be construed as surrender.
There is a high level of agreement that Gen de Chastelain is well qualified for the job. A professional soldier for 40 years, he was taught early to focus his efforts on achieving the main aim of any strategy, which in this case is the securing of the agreement and a stable political settlement. Over the long and frustrating period of the Good Friday negotiations he often acted as George Mitchell's right-hand man and appears, remarkably, to have the won the trust of both sides.
He knows that David Trimble and Gerry Adams both want to see this issue resolved so they can get on with the proper business of running Northern Ireland's affairs. But even with this common determination, there are substantial differences between them and serious problems ahead.
The two governments, as well as commentators like myself, have tended to take the rather hopeful view that because so many apparently impossible obstacles have already been overcome, this too will happen with decommissioning. But anyone who has listened to the arguments knows that the issue is a litmus test for each side of the other's commitment to making the Belfast Agreement work.
Over the summer David Trimble has grown in stature as a leader for the entire community in Northern Ireland, and his opening speech to the Assembly this week underlined this. He is doing his best to leave some room for manoeuvre on the issue of weapons. But he repeats the phrase "Something must be done" like a mantra, and even his closest supporters say that his leadership of the Ulster Unionist Party would be at serious risk if he allowed Sinn Fein to take its seats on an executive before some handover of explosives and arms.
It is perfectly understandable that the broad unionist community should feel this strongly. There is still a great deal of suspicion on both sides. If Sinn Fein is to demonstrate that it is genuinely committed to peaceful politics, then the IRA must be seen to start the process of decommissioning. Otherwise the fear remains that republicans will return to violence if they do not get their way through democratic methods.
THE argument has an added emotional force since Omagh. Sinn Fein may say that the people who made and placed the bomb were nothing to do with them, but there must be concern that in the future IRA weapons and explosives could find their way into the hands of those dissidents who remain.
Against this Gerry Adams claims, and David Trimble appears to accept, that the Sinn Fein leadership is not in a position to "deliver" the IRA. Mr Adams argues that the priority must be to implement all the provisions of the Belfast Agreement, seats on the executive as of right for Sinn Fein, North-South bodies, the equality agenda, demilitarisation. When all these things are seen to happen, decommissioning will follow.
The loyalist groups share this view and have made it clear that they will not hand over any weapons in advance of the IRA doing so. They accept the argument that the agreement does not provide for decommissioning as a prerequisite for Sinn Fein taking its seats in an executive and fear that the unionists will be blamed if there is a serious crisis on the issue.
On the face of it the two positions are irreconcilable. Sinn Fein may have the text of the agreement on its side, but unionists can reasonably argue that the spirit of the accord calls for some greater generosity. At the level of Realpolitik, there is no point in pushing the issue to the point where David Trimble is isolated from even his loyal supporters or Gerry Adams is no longer able to carry the bulk of the republican movement with him.
It might be that, given sufficient time, the two men could build a basis of trust that would enable them to reach a compromise between them. But that time is not on offer, at least at the moment. Sinn Fein wants seats on the executive to be appointed without delay, to demonstrate to its supporters that there is no pulling back from the agreement. Trimble maintains that this is not possible.
That is why Gen de Chastelain's strategic skills are so important. We need him to help all sides to find an honourable way out of this impasse. It will help that the goodwill is there. Watching the enormously hopeful scenes at Stormont this week it has been possible to discern the beginning of what Seamus Mallon describes, with a sense of yearning, as "normal politics".
The exchanges in the chamber have been good-tempered. These men and women treat each other in a way that is remarkably different from the bad old days, when Stormont was characterised by the contemptuous arrogance on the unionist side and impotent anger on the nationalist benches.
David Trimble struck exactly the right note when he spoke of his wish that this should be "a pluralist parliament for a pluralist people", thus acknowledging the changes that have taken place. There is a palpable sense that Sinn Fein and the people it represents have every bit as much right to be there as David Trimble and his colleagues. Together they must share ownership and responsibility for what happens here.
It is already wonderfully easy to imagine Bairbre de Brun answering questions about proposed cuts in education or Reg Empey laying out an environment policy for the north Antrim coast. One of the delegates to Monday's meeting of the Assembly described it as "dull". If that means ordinary and workaday, it's hard to think of a more precious adjective to apply to politics in Northern Ireland. The past 30 years have given us excitement and rivers of tears. We badly need to experience some dullish times.