Statement: Polygons that are squares are rectangles.
1. Converse
2. Inverse
3. Contra-positive
A. If a polygon is not a square, then it is not a rectangle.
B. If a polygon is a rectangle, then it is a square.
C. If a polygon is not a rectangle, then it is not a square.
To my knowledge of literally devices that would be an idiom, because it is a saying for something common!!
I think maybe C? Not sure though, so don't take my word as gospel :)