Sabine Glesner A Proof Calculus for Natural Semantics Based on Greatest Fixed Point Semantics. 73-93 2005 132 Electr. Notes Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.entcs.2005.02.011 db/journals/entcs/entcs132.html#Glesner05