The Euclidean travelling salesman problem is NP-complete

@article{tspisnp-tcs4,
   apice = {TspisnpTcs4},
   author = {Papadimitriou, Christos H.},
   doi = {10.1016/0304-3975(77)90012-3},
   issn = {0304-3975},
   journal = {Theoretical Computer Science},
   number = 3,
   pages = {237--244},
   title = {The {E}uclidean travelling salesman problem is {NP}-complete},
   url = {http://www.sciencedirect.com/science/article/pii/0304397577900123},
   volume = 4,
   year = 1977
}