Subsets

• A set A is a subset of a set B (written A ⊆ B) if and only if all elements of A are also elements of B.
• A set A is a proper subset of B, written A ⊂ B, if A⊆ B and A ≠ B.
• If A is a set, with n(A) = i, then there are 2ⁱ subsets that can be formed from A, and 2ⁱ-1 proper subsets which can be formed from A.
• The empty set is a subset of every set.
• The empty set is a proper subset of every set except the empty set.
• Do some exercises on page 55.