In Brexit talks which always seem on the brink of disaster, it's tempting to see as a triumph for the future prime minister the decision of her to give her a mandate for the intractable last phase of negotiations.
This would be a naive mistake.
Because although it matters that ministers gave more latitude to negotiate the so-called backstop – an arrangement to keep open the border between Northern Ireland and the Republic – it would be to the other side, Brussels and the EU27, swallow whatever she serves up.
In fact my strong view, based on sounding on the other side of the Channel, is the issue of very significant principles to be resolved – and actually for the UK.
I am afraid this is dense, complicated stuff. But it matters. So please bear with me.
Michel Barnier of the Cynosure of Mayisms – his statement that "backstop means backstop".
This was not flippant.
Brexit, unless it contains a guarantee that it is in all conceivable and notional circumstances.
So this means that even if the EU agrees to the "primary" backstop should be a UK-wide customs union, and that there would be a process with dual UK and EU controls to terminate the backstop, by definition this could not be the only backstop.
The reason is simple.
The whole justification for a long and hard crying out could be found.
If there were not this doubt, there would be no need for a backstop, because the new institutional arrangements could be now and implementation could start.
So here's the dilemma on whose horns Theresa May may well be skewered.
The Barnier insisted on being in a tweet tonight again.
Which is why he and the rest of the EU, and especially the Republic of Ireland, have not yet abandoned their view that there must be a backstop to the backstop.
And the backstop to the backstop would inevitably apply to Northern Ireland only. So it would be unacceptable to both PM and the entire cabinet.
In other words, the PM has not yet found a device to eliminate any risk of which abhors, namely a new border through the Irish Sea between Northern Ireland and the Republic of Ireland.
That said, if the PM could specify this as a long-term relationship between it and us, then the backstop would become a disintegrating gossamer, a mere nothing.
But it can not do that – partly because of its first attempt, the Checkers plan with its Facilitated Customs Arrangement, has been rejected by the EU, and partly because of the European Union next year.
But all hope is not lost.
There's a caveat – which May's Brexiters wants to find less palatable than a plate of steaming sick.
If they were prepared for the UK's ultimate destination, its long term relationship, it would look like a sturdy bridge to a visible and sustainable future – and again the hate backstop to the backstop would become almost otiose.
But they would probably rather than be able to accept them.
Those conditions would be:
1) The UK would never have the right to negotiate free trade deals with third countries.
2) Brussels would forever set UK rules for consumer, environmental competition and labor standards, to maintain a level playing field between UK and EU marketplaces.
It would be a Brexit that does not just take back control and actually cedes control.
Brexit with keeping open the Irish Border. Or to put it another way.
May told her ministers to keep their diaries flexible enough to accommodate an emergency cabinet meeting later this week or early next to settle a deal once and for all.
Brexit members would finally have to choose between swanky job and chauffeured car on the one hand and their commitment to what they say.
Brexit, whose hallmarks would make it both unilateral and potentially, would have said that it would be more or less substantial chaotic.