ABSTRACT
Finite state transducers (FSTs) are a sort of finite state machines that, in addition to the notion of accepting or rejecting a string, generate an output string, being Moore and Mealey machines the first antecedent of this model. Indeed, FSAs can be seen as FSTs with the same input and output symbol in each transition. But while deterministic FSAs are equivalent to nondeterministic ones, this property does not hold for transducers. In addition, closure properties are more restrictive than those that hold for FSAs.
