Talk:Benacerraf's identification problem

Mistake
"the two systems differ in their answer to whether 1 ∈ 2, insofar as ≠ {∅, {∅}}." — No, the two systems agree that 1 ∈ 2, and more generally, n ∈ n + 1, since n belongs to both sets {n} and n ∪ {n}. In particular, {∅} ∈ {∅, {∅}}. Rather, the two systems differ in their answer to whether 0 ∈ 2, and more generally, n ∈ n + k for k > 1. Boris Tsirelson (talk) 07:49, 27 July 2014 (UTC)