Prove the soundness or unsoundness of the inference rule Mod

Prove the soundness or unsoundness of the inference rule, Modus Tollens, by applying a sequence of logical inference procedures. Specify the inference rule that is applied at each step. – Do NOT prove it by truth table enumeration. --

Solution

Modul tollens:

If (p implies q) is true and if q is not true then p\' (stands for negation of p) is true:

Suppose p\' is false

Then p is true

Then p implies q cant hold , as a true statement cannot imply a false one.

Hene p\' is false, as required