 
Summary: MATH. SCAND. 65 (1989), 5966
SO(2) INVARIANTS OF A SET OF 2 x 2
HELMER ASLAKSEN
Abstract.
We give an alternative proofof a result due to Sibirskii on the polynomi
SO (2, R)) acting on M(2, C) (or M(2, R)) by conjugation. We show that
terms of traces and Pfaffians, and we find a minimal basis which is
invariants in the real case.
The polynomial invariants of 0(2, C) (or 0(2, R)) acting o
by conjugation has been studied by Sibirskii [8]. In thi
invariants when restricting to SO (2, C) (or SO (2, R)). Af
version of this paper, we were informed by Professor Sibir
already been studied by him. The results in this paper are e
[10, pp. 126127], but our approach is different. We e
approach in [8], instead of using the resuls of [9].
Let {jj} be a set of invariants. We will call {jj} a basis i
expressed polynomially in the frs. We will call {jj} a fu
invariant can be expressed as a function (not necessarily a
We will call {Jj} a complete set of invariants if they separate
classes).
