The Beauville-Bogomolov-Fujiki form 
is the primitive integral quadratic
form on 
of an irreducible
holomorphic symplectic manifold, with sign chosen to be positive on Kähler
classes. For complex dimension 
, it satisfies
 |
where 
is a constant depending on 
.
Its signature is 
.
For a K3 surface it is the intersection
form on second cohomology. A line
bundle is isotropic for this form when 
.
This condition is distinct from vanishing of its entire first Chern
class.
