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: {{#ev:youtube|7ihfZ4wlgFw|||||start=563&loop=1}}
=== <math> (\forall x : P)\varphi </math> ◁▷ <math> \notneg(\exists x : P). \neg\varphi </math> ===
: {{#ev:youtube|H3HhormBWr8|||||start=450&loop=1}}

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