Darkness descended, and the lights went on at Weston Park in Staffordshire last night as the Taoiseach, Mr Ahern, and the British Prime Minister, Mr Tony Blair, tried to resolve the age-old philosophical question of the chicken and the egg.
Which comes first in this case primarily relates to IRA arms and policing. If there can be movement on one then there can be reciprocal movement on the other, but at the time of writing last night neither republicans nor the Ulster Unionists were prepared to disclose their bottom lines.
To extend the metaphor, Mr Ahern and Mr Blair would like the chicken and egg to arrive at the same time. They want Mr David Trimble and Mr Gerry Adams to reveal more or less simultaneously what they are prepared to concede respectively on policing and arms.
If that could happen, they believe, other key issues such as demilitarisation, safeguarding the institutions, criminal justice, human rights and equality matters could be relatively easily resolved.
Mr Ahern and Mr Blair would like to see the problem in classic negotiating terms, where everyone jumps together. Sinn Fein, however, is adamant that this is dangerous spin, that the real resolution lies with Mr Blair.
Republicans were hard-balling last night. It was not a question of disclosing what the IRA might do on arms - something Sinn Fein negotiators say has nothing to do with it - but of the British government fully implementing the Belfast Agreement.
By that Sinn Fein means it wants all of Patten and the consequent total revamping of the Police Act. This, republicans insist, is a matter that is solely in the hands of Mr Blair, and not Mr Trimble, irrespective of any British concerns that unionists might become alienated from the agreement if - as unionists see it - there are further concessions to republicans on policing.
Sinn Fein also wants detail on how and when the new criminal justice system will come into effect. It wants plastic bullets banned. It wants the observation posts on the south Armagh hills dismantled. It also wants implementation of several other issues.
This is what was promised in May last year when the IRA indicated that in the context of those pledges being met it would begin a process to put its arms verifiably beyond use, Sinn Fein says. If all this happened, and if Sinn Fein had cast-iron guarantees on all its demands, then it would be a matter for the IRA to decide what it should do with its arsenals.
That, according to a senior Sinn Fein source, is the nature of the arguments that Mr Adams, Mr Martin McGuinness and the other party negotiators are putting to the governments, the UUP and the SDLP. And, according to the same source, there could be no compromise.
Mr Trimble is seeking to portray these negotiations as dealing with one matter only, that of IRA weapons.
If Sinn Fein and the UUP hold absolutely to their positions then the prospects of a deal seem pretty grim. It was very difficult, the SDLP former Deputy First Minister, Mr Seamus Mallon agreed, but all was not yet lost.