Is "$--2$" by itself a valid Math expression? I inserted the following in the calculator:
$$--2$$
and the calculator gave me a result of $2$.
Is $--2$ by itself a valid Math expression, or did the calculator added $0$ or something before it (e.g.. the calculator might have turned $--2$ into $0--2$)?

$--2$ is equivalent to $-(-2)$ or $-1 \cdot (-1 \cdot 2)$.
$-1 \cdot -1$ is just $1$, so we get $1 \cdot 2$, which is equal to $2$.
