Paola Bruscoli Alessio Guglielmi Tom Gundersen Michel Parigot Quasipolynomial Normalisation in Deep Inference via Atomic Flows and Threshold Formulae http://arxiv.org/abs/0903.5392 2009 CoRR abs/0903.5392 db/journals/corr/corr0903.html#abs-0903-5392 informal publication