For ten points, identify this  eld of mathematics concerned with ex- pressing the elements of algebraic structures as linear transformations of vector spaces.
The Krull-Schmidt theorem is an important result in this branch of math- ematics which also includes the Mackey formula. In the modular type of this branch of mathematics, Maschke's theorem does not hold because a certain en- tity is not invertible. If an equivariant map exists between two vector spaces in this  eld of study, they are isomorphic examples of the namesake object of this eld of study, which is a homomorphism from a group or algebra to a set of   matrices. For ten points, identify this  eld of mathematics concerned with ex- pressing the elements of algebraic structures as linear transformations of vector spaces.
The Krull-Schmidt theorem is an important result in this branch of math-
representation theory