  Anomalies are known to appear in the perturbation theory for the
one-dimensional Anderson model. A systematic approach to anomalies at critical
points of products of random matrices is developed, classifying and analysing
their possible types. The associated invariant measure is calculated formally.
For an anomaly of so-called second degree, it is given by the groundstate of a
certain Fokker-Planck equation on the unit circle. The Lyapunov exponent is
calculated to lowest order in perturbation theory with rigorous control of the
error terms.
