  The slope of the beta function at a fixed point is commonly thought to be RG
invariant and to be the critical exponent gamma* that governs the approach of
any physical quantity R to its fixed-point limit: R*-R proportional to
Q^gamma*. Chyla has shown that this is not quite true. Here we define a proper
RG invariant, the "effective exponent" gamma(Q), whose fixed-point limit is the
true gamma*.
