## Geometry: Common Core (15th Edition)

I is the converse of II because the hypothesis and conclusion are swapped. Inverse: If a, b, c and d do not form a 2-by-2 calendar square, then $a+d\ne b+c$. Contrapositive: If $a+d\ne b+c$, then a, b, c and d do not form a 2-by-2 calendar square.