Editing Wang tile (section)

==Generalizations==
Wang tiles can be generalized in various ways, all of which are also undecidable in the above sense.  For example, ''Wang cubes'' are equal-sized cubes with colored faces, and side colors can be matched on any polygonal [[tessellation]].
Culik and Kari have demonstrated aperiodic sets of Wang cubes.<ref>{{citation
 | last1 = Culik | first1 = Karel II
 | last2 = Kari | first2 = Jarkko | author2-link = Jarkko Kari
 | issue = 10
 | journal = [[Journal of Universal Computer Science]]
 | mr = 1392428
 | pages = 675–686
 | title = An aperiodic set of Wang cubes
 | url = http://www.jucs.org/jucs_1_10/an_aperiodic_set_of
 | volume = 1
 | year = 1995 | doi=10.1007/978-3-642-80350-5_57}}.</ref> Winfree et al. have demonstrated the feasibility of creating molecular "tiles" made from [[DNA]] (deoxyribonucleic acid) that can act as Wang tiles.<ref>{{citation
 | last1 = Winfree | first1 = E.
 | last2 = Liu | first2 = F.
 | last3 = Wenzler | first3 = L.A.
 | last4 = Seeman | first4 = N.C.
 | journal = [[Nature (journal)|Nature]]
 | pages = 539–544
 | title = Design and self-assembly of two-dimensional DNA crystals
 | volume = 394
 | year = 1998
 | issue = 6693
 | doi = 10.1038/28998 | pmid=9707114| bibcode = 1998Natur.394..539W| s2cid = 4385579
 }}.</ref> Mittal et al. have shown that these tiles can also be composed of [[peptide nucleic acid]] (PNA), a stable artificial mimic of DNA.<ref>{{citation
 | last1 = Lukeman | first1 = P.
 | last2 = Seeman | first2 = N.
 | last3 = Mittal | first3 = A.
 | contribution = Hybrid PNA/DNA nanosystems
 | title = 1st International Conference on Nanoscale/Molecular Mechanics (N-M2-I), Outrigger Wailea Resort, Maui, Hawaii
 | year = 2002}}.</ref>