You can also do like:
NPC Code:
if (player.x in <16,19>) {
bleh();
}
Which would be true if the number is in between 16 and 19 but would be false if it was exactly 16 or 19 (so 16.1 and 17 would be true but 15 and 16 would be false).
You can also do:
<16,19|
|16,19>
Respectively.
Having a good knowledge of geometry helps in this (I think that is the math subject that teaches rays and all that in a number line).