1

I'm a bit confused about how Universal Instantiation works. I read that you shouldn't really plug in any value "a" for x in "For all x P(x)" unless a choice for "a" pops up in the givens but in the following proof they just select any value y. Is that allowed? Or am I misunderstanding it and they got the Y from something else. If possible could you give me a detailed scratch-work of givens and goals.

Thanks.

The Question

The Question

Answer

enter image description here enter image description here

ChemDude
  • 421
  • Well, $y$ is not much needed: it just proves that $x\subseteq A\cap B \iff (x\subseteq A$ and $x\subseteq B)$. – Berci Mar 22 '15 at 01:05
  • Well first of all there is a typo. it should be "let $y$ be an arbitrary element" as opposed to all – DRF Mar 22 '15 at 07:31

0 Answers0