. Accordingly, the user can see what arrangements are available by examining the keys:
i1 : keys arrangementLibrary
o1 = {prism, (9_3)_2, notTame, Ziegler1, Hessian, nonFano, Ziegler2, X2,
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MacLane, X3, braid, Pappus}
o1 : List
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i2 : R = QQ[x,y,z];
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i3 : A = arrangement("Pappus",R)
o3 = {x, y, z, x - y, y - z, x - y - z, 2x + y + z, 2x + y - z, 2x - 5y + z}
o3 : Hyperplane Arrangement
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i4 : poincare A
2 3
o4 = 1 + 9T + 27T + 19T
o4 : ZZ[T]
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i5 : isDecomposable A
o5 = false
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i6 : A = arrangement("prism", ZZ/101) -- can also specify coefficient ring
o6 = {x , x , x , x , x + x + x , x + x + x }
1 2 3 4 1 2 4 1 3 4
o6 : Hyperplane Arrangement
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i7 : ring A
ZZ
o7 = ---[x , x , x , x ]
101 1 2 3 4
o7 : PolynomialRing
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