2. Specifying that all four sides are equal is not enough.

To be certain that a square is what is understood you may need to specify that all the interior angles are the same. But this is not the only way to describe a square. You can also say that it is a four-sided shape with all of its sides equal and one of its interior angles 90°. Although it is true that all four interior angles are equal to 90°, specifying that one of the interior angles is 90° forces the four-sided shape with all sides equal to be a square.