1. In a plane, a set of parallelograms with equal adjacent sides is a diamond.
2. ① A quadrilateral with four equal sides is a diamond.
3. ② The parallelogram whose diagonals are perpendicular to each other is a diamond (the parallelogram whose diagonals are perpendicular to each other and bisected is a diamond).
4. ③ A group of parallelograms with equal adjacent sides is a diamond.
5. ④ The parallelogram whose diagonal bisects a group of diagonals is a diamond.
