Thus, A + (B + C) = (A + B) + C.
If D is a set, then the power set of D is the set PD of all the subsets of D. That is,
PD = {A: A ⊆ D}
The operation + is to be regarded as an operation on PD.
1 Prove that there is an identity element with respect to the operation +, which is _________.
2 Prove every subset A of D has an inverse with respect to +, which is _________. Thus, 〈PD, +〉 is a
group!
3 Let D be the three-element set D = {a, b, c}. List the elements of PD. (For example, one element is {a},
another is {a, b}, and so on. Do not forget the empty set and the whole set D.) Then write the operation
table for 〈PD, +〉.
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