I would like to negate the following:
$\exists x, \forall y, \forall z ((F(x,y) \land G(x,z)) \rightarrow H(y,z))$
Would the following proposed solution be correct?
(1) First simplify what is in the brackets –
$((F(x,y) \land G(x,z)) \rightarrow H(y,z))$
$(\lnot(F(x,y) \land G(x,z)) \lor H(y,z))$
(2) $\forall x, \exists y, \exists z \lnot ( \lnot(F(x,y) \land G(x,z)) \lor H(y,z)) $
$\equiv \forall x, \exists y, \exists z((F(x,y) \land G(x,z)) \land \lnot H(y,z))$
Best Answer
The negation of $P \Rightarrow Q$ is $$\neg(P \Rightarrow Q) \equiv (P \wedge \neg Q)$$ and the negation of "for all" is $$\neg (\forall x)(P(x)) \equiv (\exists x)(\neg P(x)).$$ Similarly, $$\neg (\exists x)(P(x)) \equiv (\forall x)(\neg P(x))$$ so your answer is correct.