Journal of Statistical Physics, Vol. 67, Nos. 5/6, 1992. p. 1117-1149.
We try to prove rigorously that the perimeter of the large Witten-Sander cluster does not scale as the square root of its area, by making a forced comparison with the ill-posed Hele-Shaw problem of fluid dynamics. The attempt is not completely successful; nevertheless some interesting consequences of the comparison are derived.