An if that works both ways. "If and only if." Usually written "iff" to be clear.

An if, in English, can be either biconditional or conditional, depending on context.

A conditional if:
If you add a writeup, you will gain experience.

But gaining experience doesn't necessarily mean you added a writeup. There are other ways to get experience.

A biconditional if:
If you confess, we will stop torturing you.

The torturer here implies a biconditional if. They won't stop torturing for any other reason. (Well, maybe they would, for unexpected reasons, but that's external). If they stop torturing, it is safe to deductively conclude that you confessed.

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