{
Argument=x1,x2
Fit_var=a0,a1,a2,b0,b1,b2
Expression=(a0+a1*x1+a2*x2)/(b0+b1*x1+b2*x2)
}
{
Argument=x1,x2
Fit_var=a0,a1,a2,a3,a4,a5,b0,b1,b2,b3,b4,b5
Expression=(a0+a1*x1+a2*x2+a3*x1*x2+a4*x1*x1+a5*x3*x3)/(b0+b1*x1+b2*x2+b3*x1*x2+b4*x1*x1+b5*x3*x3)
}