Hello,

Does anybody know a reference for the following result: $d\ge 5$ points of $\mathbb P^2$ fail to impose independent conditions on curves of degree $d-3$ if and only if at least $d-1$ of these points are collinear. As usual, "fail to impose independent conditions" means $h^0(\mathcal I_D(d-3))>h^0(\mathcal O_{\mathbb P^2}(d-3))-d$, where $D$ is the set of points in question.

I have written up a proof of that, but of course one should give a reference if there is one, which is in my opinion quite probable.

Thank you in advance,

Serge