Consider a SIM controlled by regulator X which activates downstream genes Zi, i= 1 .. n genes with thresholds Ki. At time t=0, X begins to be produced at a constant rate β. (a) Are there biological reasons that favor placing the thresholds Ki much smaller than the maximal level of X? Consider the case in which X is an activator that begins to be produced at time t=0, and consider the effects of cell-cell variations in the production rate of X. (b) Would a design in which X is a repressor whose production stops at time t=0 provide more robust temporal programs? Explain.