Before revision:  If F: 0,^2 which measures the approximability of the associated problem \max\{F(x):x\in P\}, for solvable downwards-closed polytopes P.
After revision:  If F: multilinear extension of such functions. We introduce a new parameter for functions F\in{\bf C^2 which measures the approximability of the associated problem \max\{F(x):x\in P\}, for solvable downwards-closed polytopes P.