Robinson, Raphael M. (1971). "Undecidability and nonperiodicity for tilings of the plane". Inventiones Mathematicae. 12 (3): 177–209. doi:10.1007/BF01418780. ISSN0020-9910.
Robinson, Raphael M. (1971). "Undecidability and nonperiodicity for tilings of the plane". Inventiones Mathematicae. 12 (3): 177–209. doi:10.1007/BF01418780. ISSN0020-9910.