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### Problem with HOMFLY polynomial of a link

I am trying to compute the homfly polynomial of some links, given as braids, and I am running in some problems.

For example:

b = [3, 2, 1, 6, 5, 4, 3, 2, -3, -4, 3, -7, 5, 4, 7, -2, -3, -4, -5, -6, -1, -2, -3, -4, -5, -6, -7, 7]
Br = BraidGroup(8)
B = Br(b)
L.homfly_polynomial()


and I get the following error:

---------------------------------------------------------------------------
SignalError                               Traceback (most recent call last)
<ipython-input-7-b500a53dcd1e> in <module>()
3 braidd = Br(b)

normalization)
2630             s += ' {} {}'.format(i, cr)
2631         from sage.libs.homfly import homfly_polynomial_dict
-> 2632         dic = homfly_polynomial_dict(s)
2633         if normalization == 'lm':
2634             return L(dic)

/home/user/SageMath/local/lib/python3.7/site-packages/sage/libs/homfly.pyx in
sage.libs.homfly.homfly_polynomial_dict (build/cythonized/sage/libs/homfly.c:1471)()