Frieze groups are a mathematical concept used to explain patterns or symmetries arising in various forms of art including wallpaper and architecture. The term frieze refers to the band of decorative designs around a ceiling or another piece of work on a building. Frieze groups are very similar to the frieze form of architecture since …
While this comment could have been absorbed into the previous comment on this section, it is important to note that Hungerford specifies that does not imply that for every when dealing with groups and normal groups.
This section is rather interesting. There exist normal subgroups which have cosets which resemble abelian subgroups.
This final section of 8.1 deals with finite groups and their structures. This section is about finding isomorphisms between finite groups.
Section 8.1 has many parallels to the material previously seen in Hungerford’s book. Union of cosets (Theorem 8.4) and the notation used in Lagrange’s Theorem (|G|=|K|[G:K]) are new. These two are also some of the most difficult concepts. What does this new notation mean?
In this section Hungerford introduces cycle notation. Though it is an simple way to write groups compared to the recently introduced notation, it requires practice to assimilate. Many times Hungerford mentions permutations, but what does it mean for to be both even and odd?
This section contains much of the same principles of isomorphism as rings. There are a few ideas that are new for example: If G is abelian and H is nonabelian, then G and H are not isomorphic.
The idea that a subgroup can generate the original group is an interesting idea. The definition of a subgroup doesn’t mention anything about infinite subgroups, so they should be a possibility. (Later they are explicitly mentioned but only with cyclic subgroups.)
This section is fascinating. It establishes some of the basic properties of groups, but the one that I find particularly interesting is in Theorem 7.8 on the order of elements. Each element may be the identity element if acted upon by itself enough times
In the first part of Section 7.1 there was an emphasis that Groups only have one operation, addition. Yet here we see that there is another operation, multiplication. So why does Hungerford go through all the trouble of defining addition as the only operation in a group when a page later this changes?