  In this paper we discuss the BRST-quantization of anomalous 2d-Yang Mills
(YM) theory. Since we use an oscillator basis for the YM-Fock-space the anomaly
appears already for a pure YM-system and the constraints form a Kac-Moody
algebra with negative central charge. We also discuss the coupling of chiral
fermions and find that the BRST-cohomology for systems with chiral fermions in
a sufficiently large representation of the gauge group is completely equivalent
to the cohomology of the finite dimensional gauge group. For pure YM theory or
YM theory coupled to chiral fermions in small representations there exists an
infinite number of inequivalent cohomology classes. This is discussed in some
detail for the example of $SU(2)$.
