Set

∅ = { }

A = {∅}; |A| = 1;

B = {{a, b, c}, {x}, y, z, x}; |B| = 5

element {a, b, c} ∈ B, {x} ∈ B, y ∈ B, z ∈ B, x ∈ B

C = {{{∅}}}; |C| = 1;

subset

proper subset

排除完全相同的可能性。

power set

聯集交集的元素個數運算