  Tree transducers are formal automata that transform trees into other trees.
Many varieties of tree transducers have been explored in the automata theory
literature, and more recently, in the machine translation literature. In this
paper I review T and xT transducers, situate them among related formalisms, and
show how they can be used to implement rules for machine translation systems
that cover all of the cross-language structural divergences described in Bonnie
Dorr's influential article on the topic. I also present an implementation of xT
transduction, suitable and convenient for experimenting with translation rules.
