Techniques of proof V: Contrapositive method
If it isn’t hurting, it isn’t working.
Prime Minister John Major’s comment after being told that his government’s policies were hurting the country
The contrapositive method is very confusing to grasp initially – however, one student told me that she liked using it as it made her feel that she had done something clever. I think this feeling comes from the fact that the method is very indirect.
We saw in Chapter 8 that the statement ‘A B’ is equivalent to ‘not B not A’. The contrapositive ...