@article{IM_1971__12_142073,
     author = {Raphael M. Robinson},
     title = {Undecidability and {Nonperiodicity} for {Tilings} of the {Plane.}},
     journal = {Inventiones mathematicae},
     pages = {177--209},
     year = {1971},
     volume = {12},
     zbl = {0197.46801},
     url = {http://geodesic.mathdoc.fr/item/IM_1971__12_142073/}
}