The UK will leave the EU on October 31. That statement seems unambiguous. The problem is that there is no prospect that all of the hundreds of detailed arrangements will be ready for the change that will come on November 1.
Unless there is a still unplanned late deal between the UK and EU, for Northern Ireland businesses, waking up on November 1, the rules and practices for conducting north-south business will be uncertain.
The UK government has announced that for Northern Ireland businesses importing goods from the Republic, temporarily there will be no import tariffs.
That would not be a legally tenable longer-term answer.
The Irish government (with no backstop in place) is legally expected to collect EU import duties on exports from Northern Ireland to the Republic.
Some form of temporary expedient to facilitate trade across the border remains to be devised.
Leaving the EU on October 31 is the default legal position. The practical problems from leaving the EU can be expected to last at least two further years or even longer.
The CBI in a UK-wide analysis of what still needs to be done to deliver the practical separation from the EU has identified over 200 topics where new UK and EU arrangements are desirable. As a guide for businesses, this is well presented in straightforward language and is now available for anyone to read.
Having set out an agenda of over 200 business-relevant decisions which are still needed, the CBI - as a specific area of concern for Northern Ireland - calls for joint action if there is still no formal withdrawal deal to ensure a seamless break by the UK government, the EU Commission and the Irish government as well as involving the Northern Ireland political parties.
They are asked to "immediately enter emergency talks to provide temporary resolution for Northern Ireland". The CBI adds as a guiding statement the hope that there will be no hardening of the Irish border.
The CBI argues that it is not possible to avoid negative consequences for Northern Ireland:
"It is an utterly unsustainable position for the island and it will be essential for talks to resume as soon as possible," it says.
As a consequence of the uncertainty about trading rules, the CBI draws attention to the possibility of a boost to smuggling across the border because of tariff differentials.
The present uncertain imbalance in cross-border trading rules may fuel crime between north and south, widening the scope for incentives to avoid legal duties. Smuggling of beef, cheese and butter could take place.
Perhaps the biggest uncertainty if there is no agreed deal is the more widespread disruption, or threat of disruption, to supply chains which cross the Irish border both ways. In the language of the earlier disputes, this potential disruption is the reason for the invention of the backstop clause in the so far unapproved withdrawal agreement.
The CBI underscores again the damage this could do to both Irish economies and, with more hope than expectation, argues this calls for the governments and politicians to work closely if there is no deal and for this to be "one of their top priorities to resolve if no deal occurs".
Undertaking a wider review of issues, particularly affecting Northern Ireland, the CBI looks at the potential significance of the Common Travel Area for the UK and Ireland.
This points to the wider range of individual rights that have been agreed as part of the CTA.
The CBI also reviews the worries about the impact of no deal on the operations of the Integrated Single Electricity Market where it has identified potential concerns about a reduction in the benefits it should offer.
The CBI review presents a clear-cut set of challenges that a wider public audience will face.