  Let $W(x,y) = a x^3 + b x^4 + f_5 x^5 + f_6 x^6 + (3 a x^2)^2 y + g_5 x^5 y +
h_3 x^3 y^2 + h_4 x^4 y^2 + n_3 x^3 y^3 + a_{24} x^2 y^4 + a_{05} y^5 + a_{15}
x y^5 + a_{06} y^6$, and $X=\frac{\partial W}{\partial x}$, $Y=\frac{\partial
W}{\partial y}$, where the coefficients are non-negative constants, with $a>0$,
such that $X^{2}(x,x^{2})-Y(x,x^{2})$ is a polynomial of $x$ with non-negative
coefficients. Examples of the 2 dimensional map $\Phi: (x,y)\mapsto
(X(x,y),Y(x,y))$ satisfying the conditions are the renormalization group (RG)
map (modulo change of variables) for the restricted self-avoiding paths on the
3 and 4 dimensional pre-gaskets. We prove that there exists a unique fixed
point $(x_f,y_f)$ of $\Phi$ in the invariant set $\{(x,y)\in R^2\mid x^2\ge
y\}\setminus\{0\}$.
