In a recent paper it was proposed that for some nonlinear shell models of
turbulence one can construct a linear advection model for an auxiliary field
such that the scaling exponents of all the structure functions of the linear
and nonlinear fields coincide.
The argument depended on an assumption of continuity of the solutions as a
function of a parameter. The aim of this paper is to provide a rigorous proof
for the validity of the assumption. In addition we clarify here when the swap
of a nonlinear model by a linear one will not work.Comment: 7 pages, 4 figures, submitted to Nonlinearit