
The moduli space M(r,c_1,c_2) of Gieseker-semistable sheaves on a K3 or abelian surface admits a birational symplectic involution induced by taking dual sheaves when c_1=0. In this talk, I will first discuss when this involution becomes regular and then focus on the case M(3,0,6) for a K3 surface. I will give a local description of the involution on M(3,0,6) using quiver varieties and show that the involution quotient gives rise to a new example of an irreducible symplectic variety of dimension 20 with only isolated singularities. This is a joint work with Hsueh-Yung Lin.