BRUSSELS, BELGIUM (AFP) - The European Commission and the British government let out an audible sigh of relief on reaching Friday's historic Brexit divorce terms deal.
Yet numerous questions remain on the future trade relationship between the EU 27 and the bloc's departing member as the discussions now move on to a new phase at a December 14-15 Brussels summit.
The EU's chief Brexit negotiator Michel Barnier warned "there is still work to be done" to "consolidate" the progress made to date.
The preamble to the 15-page divorce deal published after British Prime Minister Theresa May's morning dash for talks with European Commission President Jean-Claude Juncker illustrates the still precarious nature of the deal.
"Under the caveat that nothing is agreed until everything is agreed, the joint commitments set out below in this joint report shall be reflected in the Withdrawal Agreement in full detail," says the introduction to the text.
The conclusion notes that the deal is conditional on "an overall agreement under Article 50 on the UK's withdrawal, taking into account the framework for the future relationship, including an agreement as early as possible in 2018 on transitional arrangements".
Even Friday's deal itself leaves elements open to question surrounding the thorny issue of the Irish border post-Brexit, along with the size of Britain's divorce bill and the protection of expats' rights.
The deal is clear on guaranteeing the post-Brexit rights of Britons already living in the bloc and of their EU counterparts based in Britain with family members able to claim residence.
But there is no mention, for example, of future spouses.
"We demand before we can give green light to the withdrawal agreement, that... the future free movement and residence of UK citizens will also be guaranteed and this in all 27 Member States," said Guy Verhofstadt, leader of the liberals group in the European Parliament.
It is not yet clear if British expats will be able to retain their full current rights when they move to another EU country.
Regarding citizens rights, the divorce bill text indicates Britain will bring forward a bill to incorporate them into UK law.
On adoption, the bill's provisions in relation to citizens' rights "will prevail over inconsistent or incompatible legislation, unless Parliament expressly repeals this Act in future".
But it is not clear what will happen if Westminster actually one day repeals the bill.
"Any change by UK parliament to citizens' rights will be very visible and can only happen via express repeal of treaty," was how Stefaan de Rynck, a member of the EU negotiating team, commented on Twitter.
HOW MUCH WILL IT COST?
There are also elements of ambiguity as to the exact size of the divorce bill, despite the methodology having been agreed to determine how deep Britain must delve into its pockets.
"We cannot calculate exactly the sums in question - all these figures will fluctuate," says Barnier, although unofficial EU estimations are in the order of 60 billion euros (S$96 billion).
Britain puts the sum at between 40 and 45 billion euros, though that does not include items such as an EU-guaranteed loan for Ukraine, which could generate costs for all current EU members - Britain included.
Then there is the issue of the border between Northern Ireland and the Republic of Ireland, which almost scuppered the deal over concerns in the North that Britain was headed for a deal entailing a 'hard' border separating the former from the rest of the United Kingdom.
In the agreement, the United Kingdom says it "remains committed to protecting North-South cooperation and to its guarantee of avoiding a hard border" between the two.
Britain said if that was not possible, it would propose "specific solutions to address the unique circumstances of the island of Ireland," including alignment with the Internal Market and the Customs Union rules, while respecting the terms of the Northern Ireland peace agreement.
EU President Donald Tusk has already warned that "the most difficult challenge is still ahead".
And Jonathan Powell, chief of staff to former British prime minister Tony Blair, suggests squaring the circle may prove a tall order.
"The language on 'full alignment' means different things to different people," Powell told the Financial Times.
"A series of contradictory undertakings have been given and a new separate strand of negotiation on Ireland opened in the next stage."