Rational expressions are powerful tools to define automata, but often restricted to single-tape automata. Our goal is to unleash their expressive power for transducers, and more generally, any multitape automaton; for instance
(a + |x+b + |y) ∗ . We generalize the construction of the derived-term automaton by using expansions. This approach generates small automata, and even allows us to support a composition operator
