We say a symmetric divisor on $\bar{M}_{0,n}$ is a symmetric F-divisor if $D . F_{I_1,I_2,I_3,I_4} \geq 0$ for every F curve.
In the example below, we see that for $n=8$, the divisor $3B_2+2B_3+4B_4$ is a symmetric F-divisor, while the divisor $B_2$ is not.
i1 : D=symmetricDivisorM0nbar(8,3*B_2+2*B_3+4*B_4)
o1 = 3*B + 2*B + 4*B
2 3 4
o1 : S_8-symmetric divisor on M-0-8-bar
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i2 : isSymmetricFDivisor(D) o2 = true |
i3 : D=symmetricDivisorM0nbar(8,B_2)
o3 = B
2
o3 : S_8-symmetric divisor on M-0-8-bar
|
i4 : isSymmetricFDivisor(D)
This divisor has negative intersection with the F curve F_{3, 2, 2, 1} (and maybe others too)
o4 = false
|
The object isSymmetricFDivisor is a method function.