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# Discrete Maths - Establishing an inference rule known as constructive dilemma watch

1. How would you do the lower two questions, with workings shown? (I'm not very good at discrete maths :l)
Very very grateful for any answers, pointers or help - Thanks in advance

Part 1
Establish the inference rule known as constructive dilemma which states that from the two hypotheses (P=>Q and R=>S) and (P or R) we can infer (Q or S).

[Hint: you will need to construct a truth table with 16 rows]

Part 2
Use the rules of inference to show that if A, B, C and D are propositions, the conclusion C or (not D) can be inferred from the four hypotheses , A=>B, B=>(not D), A, B=>C.

and btw,
The => symbol was meant to be an arrow symbol (but I couldn't find the keyboard short-cut!) meaning "implies". so (P=>Q) is P implies Q.
THANKS for any help!!

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