 
Summary: Rings and Algebras Problem set #2. Sept. 22, 2010.
1. Show that the converse of Schur's lemma does not hold.
2. Let V be a vector space over a field K. Show that R = End(VK ) is left primitive but not
necessarily simple. Describe the ideal structure of R.
3. Show that if R = End(VK ) as above then R has a minimal left ideal and conclude that every
simple faithful left Rmodule is isomorphic to RV .
4. Let R be a left primitive ring and 0 #= e # R an idempotent element. Show that S = eRe is
also left primitive.
5. Show that for K a field of characteristic 0 the Weylalgebra A 1 (K) = K#x, y#/(xy  yx  1) is
left primitive.
6. Decide whether the following implications are true:
a) A ring R is left primitive if and only if the full matrix ring M n (R) is left primitve.
b) A ring R is prime if and only if the full matrix ring M n (R) is prime.
7. a) Suppose the path algebra KG is finite dimensional. Give a precise condition for KG to
be primitive (prime, resp.).
b) Show that KG (without the assumption on the dimension) is prime if and only if for each
pair of vertices i, j in G there is an (oriented) path from i to j.
8. Show that the fact that R # End(VD ) is 1transitive does not imply that R is dense in End(VD )
(although it follows that V is a simple faithful Rmodule). (Hint: Construct an example where
End(RV ) is strictly larger than D.)
