Tarski's least fixed point theorem: A predicative type theoretic formulation

Abstract

We provide a type theoretic treatment of the paper "On Tarski's fixed point theorem" by Giovanni Curi. There are benefits to having a type theoretic formulation apart from routine implementation in a proof assistant. By taking advantage of (higher) inductive types, we can avoid complicated set theoretic constructions. Arguably, this results in a presentation that is conceptually clearer. Additionally, due the predicative admissibility of (higher) inductive types we take a step towards the "system independent" derivation that Curi calls for in his conclusion. Finally, we explore a condition on monotone maps that guarantees they are `generated' and give an alternative statement of the least fixed point theorem in terms of this condition.