Achieving cooperativity: the right-hand side of condition \ref{815146} as a function of the parameter 2, for different values of \(x_1\). These are profiles of the full 3-dimensional graph. The expression is symmetric between the two parameters, and so they are interchangeable in this graph. The minimal value attainable is ½, although this happens only for \(x_1\)=1, which is physically unreasonable.