control of the magnitude of  F near $\b{b}=0.$ However, if the proton is black for central collisions one can expect $F(x,\b{0})$ to show little x-dependence. (Here x plays the role that $s$ does for the hadronic collisions discussed above.) The authors of Ref.27 suggest looking at the b-dependence of

$$\Delta_{eff} = {d \ell n F(x,b)\over d \ell n 1/x}.\eqno(3.2)$$

Unitarity constraints can be expected to show up as smaller values of $\Delta_{eff}$ near $b=0.$ More quantitatively, unitarity limits at $b=0$ would give

$$\Delta_{eff}(b=0) < 2(\alpha_P-1).\eqno(3.3)$$

This is a clever idea, and it will be interesting to see what the data give.

Large mass ${\gamma}^*$ diffractive dissociation
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The traditional picture of large mass diffraction dissociation at small values of x is shown in Fig.4, where Dokshitzer, Gribov, Lipatov, Altarelli, Parisi (DGLAP)\[30-32\] evolution takes one from the hard scale Q to the soft scale $\mu$ where a soft diffractive scattering, represented by soft pomeron exchange, occurs. In Fig.4, one assumes the DGLAP ordering

$$\mu^2 \approx \b{k}^2 << \cdot\cdot\cdot << \b{k}_2^2 << \b{k}_1^2 <<
Q^2.\eqno(3.4)$$

However, this is a subtle process and it is worthwhile looking carefully at the argumentation that leads to the size of $\b{k}^2$ at the lower end 