Variables in math don't have a specific value and can be anything, but the variables in this class have specific values and always mean something.
The two scopes are for all sprites and for this sprite only.
A variable can only have one value at a time.
It won't work because after the first one changes, the other one will "change" but it will change, but it will change to itself, so it truely doesn't really ever change.
The temp variable is temperarely holding one of the values, so value 1 and value 2 can switch.