What have I learned from the PM about the detail of what Brexit means, on this her first big summit?
Well, she told us it means British control over immigration into the UK - but not via the points-based system advocated by her foreign secretary Boris Johnson and his colleagues in the campaign to take us out of the EU (this is a system that almost automatically allows foreigners to live and work here if they have certain skills; she slapped it down in a chat with hacks with all the calculated brusqueness of a migration-weary ex Home Sec).
She also refused to sign up to Johnson's and Vote Leave's assertion that Brexit would mean we would never again pay a penny or euro to Brussels. So in case you were still in any doubt, Vote Leave's pledge that Brexit would lead to an extra £350m a week for the NHS is for the birds (as all serious analysts - the detested "experts" - said it was).
So that is what Brexit won't be. Any hint of what it might be?
Well my sources tell me immigration flows will - as far as possible - be determined by two factors: the needs of businesses, public services and the economy; and an assessment of the vacancies that cannot be filled by indigenous Brits.
What the mechanism to deliver this labour-market nirvana might be I can't say - because I don't know, and nor (I fear) do ministers yet.
But what is clear is that for May the priority is to deliver British control over who comes to Britain, and NOT to limit migration flows to some specific numerical target.
What about our vital future trading arrangements with the EU and the rest of the world?
Well I refer you back to something I wrote a few weeks ago, which says we're aspiring to a goods and services free-trade deal that builds on the arrangements agreed (but not officially ratified) between Canada and the EU.
Now I don't think you'll hear May or the Brexit minister David Davis (who is talking about this in the Commons today) actually say we want "Canada with a services add-on" - because what they'll insist is that the size and shape of our economy and our long history of EU membership mean our deal will be sui generis, unique.
But it's useful shorthand to think of our likely future trading pact with the EU as "Canada-plus", simply because May has concluded that being more integrated into the EU single market, as Norway and Switzerland are, is likely to be proscribed.
How so? Well that's because of how she wants to manage immigration, and how she aims to eliminate "compulsory" financial contributions to Brussels (note ministers haven't ruled out voluntary payments that yield a clear specified benefit).
So what will Brexit actually mean?
Well anything T May chooses it to mean in the next five or six months - and then (of course) what the 27 EU members then choose to endorse or reject in her wish list, during negotiations followed by interpretation and implementation that will drag on for many many years.