Full Idea
First-order logic is the strongest complete compact theory with a Löwenheim-Skolem theorem.
Gist of Idea
First-order logic is the strongest complete compact theory with Löwenheim-Skolem
Source
Ian Hacking (What is Logic? [1979], §13)
Book Reference
'A Philosophical Companion to First-Order Logic', ed/tr. Hughes,R.I.G. [Hackett 1993], p.245