Officials from Ireland, the European Commission and UK have been trawling through 142 areas of north/south co-operation during weeks of side talks to the formal Brexit negotiations.
The sheer number of areas being examined - everything from energy to environmental management - shows the complexities facing negotiators from both the EU and UK sides as they work to ensure the Good Friday Agreement, and the all-island engagement built up over the last 20 years, is maintained in the context of the UK's EU withdrawal.
Diplomats and civil servants - including from Northern Ireland - have been meeting in Brussels on a near weekly basis for a number of days at a time since the start of October.
They're studying all the economic and social aspects of cross-border co-operation.
The work is dense and complex. Of those 142 areas which have been tabled by the British, officials must determine which ones are inextricably linked to, or are affected by, EU law and policy.
They include issues such as environmental protection, agriculture, animal health, healthcare, the single electricity market, the management of waterways, co-operation on fisheries, with a focus on Lough Foyle and Carlingford Lough, cross-border funding and the all-island bodies agreed under the Good Friday Agreement.
Security co-operation is excluded, as this will be dealt with separately.
The work is being led on the Irish side by the Ireland, United Kingdom, and Americas Division in the Department of Foreign Affairs & Trade, with input from other departments depending on the issue being examined.
At present, it's a technical exercise with officials painstakingly going through the list to pin point the truly thorny issues - areas that are currently fundamentally embedded within EU policy and legislation.
The purpose of the task is to ultimately look for ways in which co-operation in these areas can continue, when one jurisdiction is outside of the EU.
"It's like unbaking a cake," says Dr Katy Hayward, Reader in Sociology at Queen's University, Belfast, and an expert on European integration on cross-border relations on the island.
"You've got several elements to it - one is of course what has been devolved to Northern Ireland, and then you have the dimensions across the border.
"If you look at the Good Friday Agreement, it names 12 areas of co-operation. They includes areas like health, research and education, social security, environment, agriculture, so those headline areas are ones where we have seen the most impact from EU membership.
"It ties not just to legislation and harmonisation and matching of standards and regulations, but it also ties to European funding of projects."
Foreign Affairs Minister Simon Coveney has starkly set out the difficulties facing negotiators looking at these issues
"In at least half of those cases, the assumption, and in some cases the actual language, confirms that north/south co-operation is based on both jurisdictions being part of the same union, and operating to the same rule book," the minister told a recent Brexit event organised by AIB.
"In the absence of that, north/south co-operation, on a balanced basis, seems very, very difficult to design. For a start it is going to require maintenance of equivalence or some sort of mirroring system of regulation north of the border.
"And without devolved government ... that seems to me to be impossible."
Despite being dealt that mission impossible, officials continue the technical work. The two sides are also preparing for a resumption of formal talks next week, with the financial bill expected to dominate.
The conclusions reached in these technical discussions will filter into the formal Brexit talks, although the Irish Independent understands that that will be in the second phase of the negotiations, rather than this current stage, as they centre on the functioning of the future relationship.
Dr Hayward says the side talks show the importance being placed by negotiators on the issue of cross-border co-operation.
But she adds: "There is a danger that if you're thinking too rigidly about a particular area and how you can continue that outside of the European context, that it becomes a bit too much about the detail of the institutional structural side of it, and too little about the principle of the good British-Irish relationship and north/south connections.
"What's happened is that the border has become increasingly conceived of as an issue of practicality, and finding technical solutions to it," Dr Hayward believes.
"This really sets aside so much of the reality of what cross-border co-operation is today, which is about it being normal and of mutual interest at a very local grass roots level."