- $S=\NS(X)$ denotes the Néron-Severi lattice of the $K3$ surface $X$.
- $\LL$ denotes an even hyperbolic lattice.
- $\pl$ denotes the positive cone of $\LL$.
- $\ps$ denotes the positive cone of $S$.
- Denote by $\overline{C}$ the topological closure of a set $C$.
