Lattice of subgroups

Definition
The lattice of subgroups is a lattice (that is, a special kind of partially ordered set) whose elements are the subgroups are where the partial order is subgroup inclusion. Important points about this lattice:


 * The meet operation in the lattice is intersection of subgroups
 * The join operation in the lattice is join of subgroups
 * The lattice is bounded, with the upper bound being the improper subgroup (or the whole group) and the lower bound being the trivial subgroup.
 * The lattice is a complete lattice, that is, the meet and join operation can both be performed for infinitely many elements.