I have premises (1) (2) (3) and conclusion ( ) r I've checked that the argument is valid. But I still cannot find a way to show it by using rules of inference. please...
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Which exactly system of inference rules are you using? See this sticky thread.
something like this. List of rules of inference - Wikipedia, the free encyclopedia
Originally Posted by deniselim17 I have premises (1) (2) (3) and conclusion ( ) From (3) we get by addition. Then by material implication we get .
Another way is to have just because r is a premise and use the Deduction theorem (or Conditional Introduction).
So, premise (1) and premise (2) are not really necessary here?
That's right.
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