Effective Enumeration of Classes in a \sum_1^1 Equivalence Relation John Burgess Indiana University Mathematics Journal 1979 text pdf 10.1512/iumj.1979.28.28024 10.1512/iumj.1979.28.28024 en Indiana Univ. Math. J. 28 (1979) 353 - 364 state-of-the-art mathematics http://iumj.org/access/