Question -

Use the rule of interface to show that if A, B, C and D are proposition, the conclusion C or ~D can be interred from the four hypotheses A=>B, B=> ~D, A, and B=>C.

The 'rules' are whether they are Modues ponens, Modus Tollens, Addition, Simplification, Conjuction or Hypothetical syllogism.

My answer -

A=>B, B=> ~D, A, and B=>C.

A, and A ===>B, therefore B

B in turns implies C on one hand and ~D on the other, hence implies C and ~D and

in particular C or ~D.

Is above answer right?

Thanks,

Oz