Groups

Let $G$ be finite group with operation $\circ$ and identity element $e$.

1. For all $a, b \in G$, $a \circ b = b \circ a$.
2. For all $a, b, c \in G$, $(a \circ b) \circ c = a \circ (b \circ c)$.
3. If for $a, b, c \in G$, $a \circ b = e$ and $b \circ c = e$, then $a = c$.
4. For all $a \in G$, there exists $b \in G$ such that $a \circ b = e$.
5. If $a$ is an inverse of $b$, then $b$ is an inverse of $a$.
6. The inverse of $a \circ b$ is $a^{-1} \circ b^{-1}$.
7. For all $a$ there exists positive integer $j$ such that $a^j = a$.
8. For any positive integer $n$, there exists at least one group of order $n$.
9. For any positive integer $n$, a set of integers from $1$ to $2n$ form a group under multiplication modulo $2n+1$.

Submit a sequence of true statements, like 2 3 7 9.