Seems about right
1. A->B (premise)
2. A (premise)
3. B (modus ponens 1, 2)
4. B->C (premise)
5. C (modus ponens 3, 4)
6. B->~D (premise)
7. ~D (modus ponens 3, 6)
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
I'm not sure who this unstated 'we' is. I only showed that both C and ~D could be derived using the given premises. If you disagree, show where the derivation is wrong. Both are true under the premises and all that as far as I can see. I guess trying to help out is frowned up around here. I'll pack my swag and leave so that you (as in the unstated we) can be happy that Disjunction are not introduced. Something I didn't do. Goodbye.