Local sentences and Mahlo cardinals

Local sentences were introduced by Ressayre in [Res88] who proved certain remarkable stretching theorems establishing the equivalence between the existence of finite models for these sentences and the existence of some infinite well ordered models. Two of these stretching theorems were only proved under certain large cardinal axioms but the question of their exact (consistency) strength was left open in [FR96]. Here, we solve this problem, using a combinatorial result of J. H. Schmerl [Sch74]. In fact, we show that the stretching principles are equivalent to the existence of n-Mahlo cardinals for appropriate integers n. This is done by proving first that for each integer n, there is a local sentence φn which has well ordered models of order type τ, for every infinite ordinal τ > ω which is not an n-Mahlo cardinal. ∗ UMR 5668 - CNRS - ENS Lyon - UCB Lyon - INRIA 1 

• Type: Journal
• Year: 2007
• Where: MLQ
• Authors: Olivier Finkel, Stevo Todorcevic
• Keywords: Large Cardinal Axioms, Local Sentence, MLQ 2007, finite Models