I have no idea how to type math symbols into here so it's all in the PNG attached.(adsbygoogle = window.adsbygoogle || []).push({});

I'm probably kind of dumb for not getting this but...

I understand that 1) & 3) are true. And the 2) is not right, as it means all x are members of F and true for P(x) when we mean all xthatare members of F are true for P(x).

But why do we use 3) instead of 4)?

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# Stupid question related to proof writing.

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