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 ## Text
 - https://web.archive.org/web/20120722092427/http://journals.tdl.org/jodi/article/view/131/129
+- https://patents.google.com/patent/US6262736
+- http://www.dgp.utoronto.ca/~mjmcguff/research/zigzag-and-mSpace/zigzag-and-mSpace.pdf
 
 ## Videos
 - https://www.youtube.com/watch?v=WEj9vqVvHPc