Negative elimination

Negative elimination is basically the rule of double negatives: "it's not the case that it's not raining" means that it's raining. Likewise, it's logically consistent to claim that "it's raining" means that "it's not not raining".

Formally:

  ¬ ¬ A
  ∴ A

also

  ¬ ¬ ¬ A
  ∴ ¬ A