\b[U+D.] By <absoluteness of infinitude between transitive models>, two <transitive models> of <ZFC> agree on the <natural numbers> and therefore on whether a shared <set> is a <finite set> or an <infinite set>.

Solution

Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 121 / 1 / i / a / Solution

 Solution (source code)