1. proper subset just doesn't include the set itself. If set A = (1, 2), then set (1, 2) is not a proper subset of set A but a subset.

In other words; When B=A, b is a subset of a.

When b is less than a, it is proper subset.

2. Because the rhombus is a parallelogram and the parallelogram is not a rhombus, it can be seen that the parallelogram is greater than or equal to the rhombus. In this series,

Use tolerance to express this relationship. If a contains b, it can be understood that a is greater than or equal to B.

3. For example, 1