The Irish border after Brexit will be real but can be simplified

BRITISH prime minister Theresa May declared in her white paper on the United Kingdom’s exit from and new partnership with the European Union the following: “When the UK leaves the EU we aim to have as seamless and frictionless a border as possible between Northern Ireland and Ireland, so that we can continue to see the trade and everyday movements we have seen up to now.”
So what will that mean in practice?