> restart:
> assume(teta,real,theta>0):
> phi:=(-log(t))^theta:
> phiinv:=solve(phi=s,t);
> lambda:=2-2*limit(diff(subs(s=2*s,phiinv),s)/diff(phiinv,s),s=0);

                                       1
                      phiinv := ----------------
                                        ln(s)
                                exp(exp(------))
                                        theta~


                                       /  1   \
                                       |------|
                                       \theta~/
                      lambda := 2 - 2 2

> 
