Octadecagon and 2{9/4} or two enneagrams, {18/6} is reduced to 6{3} or 6 equilateral triangles, and finally {18/9} is reduced to 9{2} as nine digons. Deeper truncations of the regular enneagon and enneagrams can produce isogonal (vertex-transitive) intermediate octadecagram forms with equally spaced vertices and two edge lengths. Other truncations form double coverings: t{9/8}={18/8}=2{9/4}, t{9/4}={18/4}=2{9/2}, t{9/2}={18/2}=2{9}. The regular octadecagon is the Petrie polygon for a number of higher-dimensional polytopes, shown in these skew orthogonal projections from Coxeter planes: Octadecagon An octadecagon (or octakaidecagon) or 18-gon is an eighteen-sided polygon. A "regular octadecagon" has a Schläfli symbol {18} and can be constructed
Hampton Sides a BA in history. Sides lives in Santa Fe, New Mexico, with his wife Anne Goodwin Sides, a journalist and former NPR editor, and their three boys, all soccer players. He is a past fellow of Yaddo, the MacDowell Colony, and the Japan Society, and an Edwards Media Fellow at Stanford University. He is an advisory board member of the Mayborn Literary Nonfiction Conference. Sides has guest-lectured at Columbia, Yale, Stanford, SMU, Colorado College, the Autry National Center of the American West, the American Embassy in Manila, Rehoboth Christian School, and the National World War II Museum, among other venues