Reduction of Intermediate Alphabets in Finite-State Transducer Cascades
  This article describes an algorithm for reducing the intermediate alphabets in cascades of finite-state transducers (FSTs). Although the method modifies the component FSTs, there is no change in the overall relation described by the whole cascade. No additional information or special algorithm, that could decelerate the processing of input, is required at runtime. Two examples from Natural Language Processing are used to illustrate the effect of the algorithm on the sizes of the FSTs and their alphabets. With some FSTs the number of arcs and symbols shrank considerably. 
Andre Kempe