R. Niedermeier and P. Rossmanith. . Unambiguous simulations of auxiliary pushdown automata and circuits . R. Niedermeier and P. Rossmanith. Extended locally definable acceptance types . Springer , 1993.
Long version see TR below.
Journal version above. R. Niedermeier and P. Rossmanith. On the power of reading and writing simultaneously in parallel computations . R. Niedermeier and P. Rossmanith. Rep. of Germany.