Nondensity of stability for polynomial automorphisms of $\mathbb{C}^2$ Gregery Buzzard 37F1532H5032H02structurally stabledynamical degreepolynomial automorphisms Indiana University Mathematics Journal 1999 text pdf 10.1512/iumj.1999.48.1656 10.1512/iumj.1999.48.1656 en Indiana Univ. Math. J. 48 (1999) 857 - 866 state-of-the-art mathematics http://iumj.org/access/