[ Diff(x[2], t) = k[5]*x[1] + k[6]*k[7]*x[2]*(1 - k[8]*(x[2] + x[3])) - k[10]*x[2], Diff(x[3], t) = (1 - k[5])*x[1] + k[6]*k[7]*x[3]*(1 - k[8]*(x[2] + x[3])) - k[10]*x[3], Diff(x[4], t) = k[9]*x[2] - k[11]*x[4] ]