∪A—— Let A be a set containing a set, or a family of sets, and A is also called∪ A;

∪B-let b be a set containing a set, or a family of sets, and b is also called∪ b,

To illustrate this problem,

A 1 = {{ 1, 2}, {a, b }}, a2 = {{3,4}, {c, d}}, then a1∪ a2 = ∪ a.

If a? B, then b1= {1,2}, {a, b }}, B2 = {{3,4}, {c, d}}, b1∪ B2 = ∪ B.

∴∪A？ ∪B .