A Hasse diagram is used for partially ordered sets, however here it is used to show subgroup structure of a group, that is a lattice of subgroups.
For example the Hasse diagram for the D4 group, that is the dihedral group of rotations and reflections of a square.
So the whole D4 group has 8 permutations and this has 9 subgroups:
- 3 subgroups with 4 permutations.
- 5 subgroups with 2 permutations.
- 1 trivial identity permutation.
The Hasse represents a lattice which is explained on this page.