[math] \exists x \left[ \varnothing \in x \land \forall y \left( y \in x \to y \cup \{y\} \in x \right) \right] [/math]
>>17039891Most people who might complain about this don't even know that ZF + the negation of OP's claim is mutually interpretable with Peano arithmetics (or even bi interpretable iirc however this is somewhat tricky to establish although intuitive). See "the Ackermann model" (linking hereditarily finite sets and integers) for more precisions.
>>17039891>>17040009No one gives a shit.
