has vertices 1, 2, ..., n, and its edges are a list of lists of length 2. The graphic arrangement
is, by definition, the subarrangement of the type A_(n-1) arrangement with hyperplanes
i1 : G = {{1,2},{2,3},{3,4},{4,1}}; -- a four-cycle
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i2 : AG = graphic G
o2 = {- x + x , - x + x , - x + x , x - x }
1 2 2 3 3 4 1 4
o2 : Hyperplane Arrangement
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i3 : describe AG
o3 = {- x + x , - x + x , - x + x , x - x }
1 2 2 3 3 4 1 4
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i4 : rank AG -- the number of vertices minus number of components
o4 = 3
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i5 : ring AG
o5 = QQ[x , x , x , x ]
1 2 3 4
o5 : PolynomialRing
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i6 : ring graphic(G,ZZ[x,y,z,w])
o6 = ZZ[x, y, z, w]
o6 : PolynomialRing
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