Solution
= Solution
For a <divisor on an algebraic curve> $D$, define its <Riemann-Roch space> by
$$
L(D)=\{0\}\cup\{f\in\mathbb C(X)^\times:(f)+D\geq0\}.
$$
Then
$$
\boxed{\ell(D)=\dim_{\mathbb C}L(D).}
$$
= Solution
For a <divisor on an algebraic curve> $D$, define its <Riemann-Roch space> by
$$
L(D)=\{0\}\cup\{f\in\mathbb C(X)^\times:(f)+D\geq0\}.
$$
Then
$$
\boxed{\ell(D)=\dim_{\mathbb C}L(D).}
$$