tr_ubuild builds a transducer (two-level finite state automaton) from a list of word pairs, where the second word might have annotations. The format of input is:
surface_word lexical_word [annotations]
where surface_word, lexical_word and annotations are arbitrary strings that do not contain filler or annotation separator.
The output is a transducer that can be used by tr_spell, tr_accent, tr_morph, and tr_prefix.