Math Fundamentals18 sections · 814 units
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Proper Subset

Subset but not equal

Set AA is a proper subset of BB if A⊆BA \subseteq B and A≠BA \neq B. You write A⊂BA \subset B.

For example, {1,2}⊂{1,2,3}\{1, 2\} \subset \{1, 2, 3\} is true, but {1,2,3}⊂{1,2,3}\{1, 2, 3\} \subset \{1, 2, 3\} is false because they are equal.

Proper subsets exclude the case where A=BA = B. This distinction matters in proofs and problem constraints.