alt Hacker NewsFormal can be foolish, too. If you don't believe that, then I have a set for sale, with the property that it contains all sets that don't contain itself.
Formal can be foolish, too. If you don't believe that, then I have a set for sale, with the property that it contains all sets that don't contain itself.
The problem you’re referring to arose precisely due to lack of formalism. It was a problem back when mathematicians were toying with naive set theory, one not based on axioms, but instead on intuitive terminology. Moving to axiomatic, more formal, set theory solved it.