Proof by contradiction or contrapositive are both indirect proofs. For
a proof of contrapositive, we assume that the conclusion is false and
prove that the hypothesis is also false. For a proof of contradiction,
we assume that the negation of the hypothesis is true, then we find a
contradiction proving it to be false, thus proving the hypothesis true.
Here's an example of proof by contrapositive.
The claim is that for any integer a and b,
a+b≥15
implies that
a≥8
