Lecture 24 of Abstract Algebra E-222

Lecture 23 was difficult but it was the last lecture in E-222 on group theory. The remaining lectures will be on rings which are also ( abelian ) groups but with an additional operation ( multiplication ).  Purpose of the first lecture on rings was mainly to establish some definitions and show analogies between group theory and ring theory. I expect a lot of stuff on ideals in the forthcoming lectures.

Definition.
A ring is an abelian group with an additional operation * such that:
- * is closed.
- * is associative
- 1 * a = a.
This makes the ring a monoid with respect to *.
( Gross defined it slightly different in the lecture ).

Gross showed an interesting way to construct rings from abelian rings. The endomorphisms of an abelian group End(A) form a ring if an element f_a in the ring is constructed from an element a in A by taking the map f(1) = a.

Some furter topics which were introduced:


( Ideal )


( Quotient ring )


( Unit )


( Examples of groups of units )