Okay then, what happens next? The press is full of guidance as to the steps which follow the giving of notice under Article 50. First there will be a White Paper. Then Mr Tusk will send out guidelines regarding the structure of negotiations. The rest of April will be spent by the EU producing a mandate, completed at a summit on 29 April. From then on there will be negotiations, summits, walkouts and all the rest of it with a view to having an agreement ready for ratification in the autumn of 2018.
In addition, nationals of 88 non-EU countries (including Russia) working in the EU are accorded the same rights as EU citizens by agreements between these countries and the EU. Why can't Britain become the 89th such country? As far as I am aware, this possibility has never been raised by anyone in the UK. And, once again, these are agreements with the EU as a whole, not with individual EU member-states.