On Non-wellfounded Sets as Fixed Points of Substitutions
Tapani Hyttinen, Matti Pauna · Notre Dame Journal of Formal Logic · 2001
We study the non-wellfounded sets as fixed points of substitution. For example, we show that ZFA implies that every function has a fixed point. As a corollary we determine for which functions f there is a function g such that $ g = g \star f$. We also present a classification of non-wellfounded sets according to their branching structure.