You'll also see words that sound like a guarantee, things that ensure imply guarantee, always lead to something else, introduce a right side idea. And words that introduce necessity, if we're saying that we require something, we need it, we depend on it, that thing also would go on the right side on the necessary side. In fact, it's just really nice to remember that if it's required, it goes on the right. And then we have these three words, unless, until and without, where the rule that you want to memorize is that you will put whatever idea comes after that word on the left side of the arrow, but a negated version. So if not, is saying, you treat it like if, in that you put it on the left side, but you need to put the negated version. So returning to this paragraph, the first one we saw was only when, which is just like only if, it introduces a right side idea, a necessary condition.