\b[D.] <Downward absoluteness of cardinalhood> holds because, if the larger <transitive model> sees no <bijection> with a smaller <ordinal>, neither can the smaller model, whose functions form only a subset of those in the larger model. Cardinalhood is not described by an <upward absolute formula>, because the larger model can contain a new bijection collapsing an ordinal that the smaller model regards as a <cardinal number>.

Solution

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

 Solution (source code)