Put Simply, if a contradiction can be proved in Peano arithmetic, then established theory would be logically inconsistent. 「関家の森」ではなく「関さんの森」というところがいいですね。親しみを感じます。 On the other hand, The 2 definitions usually are not equal, as you'll find theorems that may be said in terms of Peano arithmetic and proved in set principle, which are https://medium.com/@cureayublog/