String Languages Generated by Total Deterministic Macro Tree Transducers

. The class of string languages obtained by taking the yields of output tree languages of total deterministic macro tree transducers (MTTs) is investigated. The first main result is that MTTs which are linear and nondeleting in the parameters generate the same class of string languages as total deterministic top-down tree transducers. The second main result is a so called "bridge theorem"; it can be used to show that there is a string language generated by a nondeterministic top-down tree transducer with monadic input, i.e., an ET0L language, which cannot be generated by an MTT. In fact, it is shown that this language cannot even be generated by the composition closure of MTTs; hence it is also not in the IO-hierarchy.