It is known that the general traveling salesman problem is NP-hard. Even when the distances follow the triangle inequality. But let's take the problem very literally. There are actual cities (points) on a 2-d euclidean space and a tour must be devised to visit all of them in the smallest total distance. We are given the $x$ and $y$ coordinates of each city and the distances between them are the euclidean distances. Is this simplified problem also NP-hard?