Mathematics for IGCSE & O level - Sets (Section 1 - No. 47)
What is the meaning of A ⊆ B?
A is a proper subset of B
A is a subset of B or A = B
B is a subset of A
B is a proper subset of A
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A ⊆ B means all elements of A are also in B, including the possibility that A and B are equal.