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show/hide this revision's text 2 Texified because the question was on the front page anyway

For most cardinals κ<λ, $\kappa \leq \lambda$, it must happen that the infinite symmetric group Sκ$S_\kappa$ satisfies exactly the same first order theory as Sλ. $S_\lambda$. That is, the groups are elementarily equivalent. This is just because there are only continuum many theories in a countable language, but more cardinals than that.

See Elementary equivalence of infinitary symmetric groups.

show/hide this revision's text 1 [made Community Wiki]

For most cardinals κ<λ, it must happen that the infinite symmetric group Sκ satisfies exactly the same first order theory as Sλ. That is, the groups are elementarily equivalent. This is just because there are only continuum many theories in a countable language, but more cardinals than that.

See Elementary equivalence of infinitary symmetric groups.