Help with discrete math proofs

[eternal ridge]

I need to use natural deduction to proof this. I can use the law of the excluded middle (LEM) or Inderect proof as classical logic tools

[icy yoke]

For 3, how can one prove that C is true?
Hint: ||Show that A or B follows, and infer that C is true.||.

[icy yoke]

Hint2: ||Recall that is X is true, then so is X or Y.||

6 is the exact same as 3, just swap A and B.

11 is simply or elimination.

[supple mural]

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