def
IsSpecialDivisor
{C : Type u_1}
{F : Type u_2}
{k : Type u_3}
[Field k]
[Field F]
[Algebra k F]
[RiemannRochData C F k]
(D : CurveDivisor C)
:
A divisor $D$ on a curve is special if its index of speciality $i(D) = \ell(K - D)$ is positive.