| Matthew Schwartz 2016 , , USA: Harvard University, Page 1, Part 1 | |
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| Itten Johannes 1970 , , Usa: David Van Nostrand Co, Page 29-31 | Matthew Schwartz 2016 , , USA: Harvard University, Page 3, Part 2 |
Matthew Schwartz 2016 , , USA: Harvard University, Page 11, Part 6.