Question

What does contrapositive mean?

Answer 1

Let
A => B
be a logical argument. Then the contrapositive of this argument is
not B => not A

It turns out that these two forms of the argument are logically identical. I.e., the truth value of one argument is identical to the other; e.g., if (A=>B) is true then (not B => not A) is true and vice versa.

Answer 2

http://en.wikipedia.org/wiki/Contraposition
This has a good description of the contrapositive

Answer 3

thx everyone