US President Donald Trump took his European allies by surprise when it became clear last week that he was considering a plan to buy Greenland from Denmark. "Greenland is a strategic place ... I'm just saying that a president who knows something about buying real estate wants to look at it," said his economic advisor Larry Kudlow. But in Europe, almost no one understands this. Danish Prime Minister Mette Frederikson has described the idea as absurd, and it has been said from Greenland itself that "it is not for sale".