Re: The set of necessary FISONs

Am 06.03.2025 um 09:54 schrieb WM: [...]

{ } ∈ Z₀, and
if {{{...{{{ }}}...}}} with n curly brackets ∈ Z₀
then {{{...{{{ }}}...}}} with n+1 curly brackets ∈ Z₀.

Right. So in math we would rather write
| {} ∈ Z₀, and for all x: if x ∈ Z₀ then {x} ∈ Z₀
(a more or less equivalent statement).