Singularities of Real Analytic Varieties Andrew Wallace Indiana University Mathematics Journal 1961 text pdf 10.1512/iumj.1961.10.10043 10.1512/iumj.1961.10.10043 en Indiana Univ. Math. J. 10 (1961) 651 - 680 state-of-the-art mathematics http://iumj.org/access/