Analogies with other conflict situations only get you so far in Northern Ireland. The Algerian analogy used to be a popular one with republicans, who drew a parallel between the unionists and the French settlers, or pieds noirs. But the unionists have been here longer than the French in Algeria and they aren't going away, you know.

More recently, republicans have preferred the South African parallel. Mr Gerry Adams was at it again in a statement yesterday in which he quoted the writer Allister Sparks' description of South Africa as "two minds, two worlds, one country".

Unionists would not agree that the island of Ireland is one country, but they would have to accept that they and republicans inhabit parallel universes.

Thus there are two completely different but equally coherent views of the decommissioning issue. Republicans hark back to the days when, as they see it, their communities were left defenceless against sectarian pogroms. There is much talk about the siege mentality among unionists, but nationalists have their own version of that mind-set and can quote from their history in Northern Ireland to justify their position.

Unionists have great difficulty, to put it mildly, with the notion of sitting down in government with people they regard as figureheads for a terrorist organisation. At the very least, they want a down-payment on total disarmament, that essential consignment of "product", be it arms, explosives, or both, to reassure them that Gerry and Martin really mean it when they say they want peace.

We have been here before. Many trees have died to provide the newsprint for journalists and commentators to tease out the decommissioning issue, which seemed such a huge roadblock to progress towards peace and reconciliation.

Republicans remain broadly unmoved by the plight of David Trimble and his supporters in the UUP leadership. As far as republicans are concerned, "the agreement is the agreement is the agreement". They also allege that the UUP is "milking" the arms issue for political gain: the unionists paint themselves into a corner on decommissioning and then Sinn Fein comes under pressure to get them out of it. In the process, the "green" elements of the agreement become fainter.

Republicans have set their face against "trading off" Semtex and weapons for a place at the cabinet table. As far as they are concerned, the agreement gives them the right to be there on the basis of their electoral mandate. They are disappointed that the initiatives they took with the Adams statement on the need for an end to violence and the appointment of Martin McGuinness to the decommissioning body have not yet been reciprocated by the formation of the shadow executive.

The firm republican message is: "We are not going to collude in the negation of our mandate. It's not on." The next move, as far as they are concerned, is up to Mr Trimble: he has to establish the executive as soon as possible. Instead of appeasing the reactionary elements in unionism, he should be drawing on the support of those members of the unionist community who demonstrated their willingness to embrace change by voting "Yes" in the referendum on the Good Friday pact.

Leaving that universe to enter the world view of the unionists is like travelling from one planet to another. The UUP leadership is said to be "very worried" about the "Dword". Senior unionists are still looking over their shoulder at Jeffrey Donaldson. Decommissioning as an issue is growing all the time and unionist attitudes are hardening. Let Dublin and London come up with what schemes they may, Trimble needs "hardware".

We have been here before: the irresistible force meeting the immovable object. Sources in the peace process, with long experience of these recurring crises, were obdurately refusing to panic last night. Both sides needed "a bit of time and space" to get around the problem. On the broader stage, significant progress had been made. The Assembly discussions this week were dignified and constructive and, instead of megaphone diplomacy, there was now a face-to-face relationship between Trimble and Adams. The two men knew they had to help each other.

"Throughout the whole history of the process there has been a series of obstacles which, if you look at them straight, seem impossible to overcome", one insider observed. "Somehow the process survived, because the political will was there and because people didn't realistically have an alternative. That's true of this situation as well."

SINN FEIN spokesmen portrayed the removal of troops from the Belfast streets as an inadequate and insufficient gesture: they should all be withdrawn. But observers saw it as a significant move nonetheless, increas ing the pressure on what Mr Trimble now calls the "republican movement" (previously known as "Sinn Fein/IRA") to take the "hard decision" eventually. The closure of British army bases in south Armagh is now a live possibility, but not until an assessment of the true intentions and capacity of the "Real IRA" has been made.

All the indications are that the Provisionals are not about to decommission weapons and explosives in the short term and certainly not in advance of the establishment of an executive. But the mandarins, who have to do what is called the "heavy lifting" in these situations, are said to be exploring the possibility that the appointment of Mr McGuinness to the decommissioning body could lead to "further steps" which, though short of the physical handing over or destruction of arms, would help to break the current impasse. "There must be some way of defusing it to buy people time", one insider said.

The good news, meanwhile, is that, according to reports, production of Semtex has ceased: demand has fallen off so much, it's no longer worth the effort.