Recently, A.A. Kirillov introduced an interesting class of associative algebras connected with the adjoint representation of G [Ki]. In our paper, such algebras are called g-endomorphism algebras. Each g-endomorphism algebra is a module over the algebra of invariants k[g]; furthermore, it is a direct sum of modules of covariants. Hence it is a free graded finitely generated module over k[g]. Th...

As mentioned several times in class, the arithmetic of quaternionic Shimura varieties is strongly controlled by the behavior of the class of CM points (just as in the case of modular curves). Just as for elliptic curves, if o is an order in an imaginary quadratic field K, one has a notion of a QM-surface with o-CM. Namely, let ι : O ↪→ A be a QM structure on an abelian surface (we are still wor...

We say the endomorphism problem is solvable for an element W in a free group F if it can be decided effectively whether, given U in F , there is an endomorphism φ of F sending W to U . This work analyzes an approach due to C. Edmunds and improved by C. Sims. Here we prove that the approach provides an efficient algorithm for solving the endomorphism problem when W is a twogenerator word. We sho...