Does anybody know any example of a semistable and nonsimple sheaf on a K3 surface $S$?
Take the 2minute tour
×
MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.
The trival sheaf $\mathcal O_S\oplus\mathcal O_S$ is one: it has nontrivial global endomorphism algebra $gl_2(k)$ and is semistable. 

