I'm facing some difficulties with a transitivity proof to show that a relation is indeed an equivalence relation.
Let $R$ be a relation on $\mathscr{P}(\mathbb{N})$ and $P, Q \in \mathscr{P}(\mathbb{N})$. Then $(P, Q) \in R$ iff $|P\triangle Q| \in \mathbb{N}$. (Here, $0 \in \mathbb{N}$) I have managed to show the two trivial cases of reflexivity and symmetry, but I'm stuck at proving transitivity for this relation.
In my understanding only the cases where $P$ or $Q$ (but not both) are equal to $\mathbb{N}$ result in $(P, Q) \notin R$. If that is correct, $(P, Q) \in R \Longleftrightarrow (|P| \in \mathbb{N} \wedge |Q| \in \mathbb{N})\vee (P = Q)$.
Is this assumption correct? If so, I'd be able to show transitivity from there. If not, how could I go about showing transitivity?