This paper (to appear in Roca, Iggy (ed.) Derivations and 
 Constraints in Phonology, Oxford Univ. Press) explores the theoretical
 consequences of surface-to-surface correspondence constraints in
 Optimality Theory, in comparison to a derivational approach
 employing sequential derivational mechanisms like cyclicity and
 ordered default rules. The empirical object of investigation are
 the facts of the g-N(angma) alternation and variation in Tokyo
 Japanese.  The central argument of the paper is that the OT
 analysis is better equipped to handle the facts of the
 alternation, which are truly intricate and interesting, since an
 (at first glance) simple process of allophony is complicated by
 subpatterns of optionality vs. obligatoriness, governed by
 factors such as the presence vs. absence of related words and the
 influence of Rendaku voicing.