Prove A is a subset of B with the ELEMENT METHOD

How can we prove that A is a subset of B? The element method has two steps. Firstly, assume that x is an element of A. Then you need to show that x is also an element of B. Because x is chosen generically, this means that every element of A is necessarily an element of B, and thus A is a subset of B. If you want to prove that two sets are EQUAL, then you need to use the element method to show that A is a subset of B AND that B is a subset of A.

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