  This paper extends the calculus of regular expressions with new types of
replacement expressions that enhance the expressiveness of the simple replace
operator defined in Karttunen (1995). Parallel replacement allows multiple
replacements to apply simultaneously to the same input without interfering with
each other. We also allow a replacement to be constrained by any number of
alternative contexts. With these enhancements, the general replacement
expressions are more versatile than two-level rules for the description of
complex morphological alternations.
