Angluin's Theorem for Indexed Families of R.E. Sets and Applications
Dick de Jongh, Makoto Kanazawa

Abstract:
We extend Angluin's (1980) theorem to characterize identifiability of indexed 
families of r.e. languages, as opposed to indexed families of recursive 
languages. We also prove some variants characterizing conservativity and two 
other similar restrictions, paralleling Zeugmann, Lange, and Kapur's (1992, 
1995) results for indexed families of recursive languages.