Michael Vielhaber Mónica del Pilar Canales Chacon Towards a General Theory of Simultaneous Diophantine Approximation of Formal Power Series: Multidimensional Linear Complexity http://arxiv.org/abs/cs/0607030 2006 CoRR abs/cs/0607030 db/journals/corr/corr0607.html#abs-cs-0607030 informal publication