ABSTRACT
Every finite nonempty set has as many subsets with an even number of elements as subsets with an odd number of elements.
Consider again the subsets of the three-element set {A,B, C}. Half of these subsets have an even number of elements and half an odd number of elements:
even number of elements odd number of elements ∅ {A}
{A,B} {B} {A,C} {C} {B,C} {A,B, C}.
