If a shape is a circle, then it is round.
It should be true, but the quality of roundness would be debated.
If a shape is round, it is a circle.
There are other examples of the quality of roundness, such as ovals.
If a shape is not a circle, it is not round.
Again, oval.
If a shape is not round, it is not a circle.
This would be true, as circles are known to be round, and the perfect circle is round.