Page 12 - Chapt1

Example 10

Let A be a set and let B = {A, {A}},

then, since A and {A} are elements

of B, we have A ∈ B and {A} ∈B. It Why?

follows that {A} ⊆ B and {{A}} ⊆ B.

However, it is not true that A ⊆ B