Venanzio Capretta Tarmo Uustalu Varmo Vene Corecursive Algebras: A Study of General Structured Corecursion. 84-100 2009 SBMF http://dx.doi.org/10.1007/978-3-642-10452-7_7 conf/sbmf/2009 db/conf/sbmf/sbmf2009.html#CaprettaUV09