enGleason, Andrew M. (), „Angle trisection, the heptagon, and the triskaidecagon”, American Mathematical Monthly, 95 (3): 185–194, doi:10.2307/2323624, MR0935432. Footnote 8, p. 191.
enGleason, Andrew M. (), „Angle trisection, the heptagon, and the triskaidecagon”, American Mathematical Monthly, 95 (3): 185–194, doi:10.2307/2323624, MR0935432. Footnote 8, p. 191.