Answer:
contrapositive
Explanation:
The converse statement would be ...
b ⇒ a
The contrapositive swaps the parts and negates them both:
¬b ⇒ ¬a . . . . . matches your given statement
The inverse negates both parts:
¬a ⇒ ¬b
A contradiction arises when the implication is false: a is true and b is false.