If I have a complete lattice $L$, what conditions do I need for $I\subseteq L$ to be an ideal?
In a general lattice the conditions are:
- $I$ is a lower set;
- $I$ is closed under (finite) joins.
For a complete lattice, do we require that $I$ be closed under arbitrary joins? Or is there a special name for such a "better" ideal?
OK, I've found the answer here. Such a "better" ideal is called a complete ideal.