Given this system of nonlinear equations, solve them by fixed-point iteration starting from $(1,-1,1)$: $$\begin{align} 9xy+y^2+3z+18&=0\tag1\\ x^2+12xy-yz+33&=0\tag2\\ 5x-4yz+z^2-26&=0\tag3\end{align}$$
How can I choose $3$ functions $f, g, h$ satisfying ,$ x=f(x,y,z), \ y=g(x,y,z) \ and \ z=h(x,y,z). $