Subset: the range of set A is greater than or equal to set B, and set B is a subset of a; Proper subset: The range of the set A is larger than that of B, and B is the proper subset of A..
Give an example to illustrate.
If the set A={s, t}, then the subset of A is: empty set, {s}, {t}, {s, t}
Proper subset of A has: empty set, {s}, {t}