Inclusion-Exclusion Principle
See the complete article on my own blog https://dyingdown.github.io/2019/08/15/Inclusion-Exclusion-Principle/
In combinatorics (combinatorial mathematics), the inclusion–exclusion principle is a counting technique which generalizes the familiar method of obtaining the number of elements in the union of two finite sets; – From Wikipedia
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Example: Set A and B
∣ A ∪ B ∣ = ∣ A ∣ + ∣ B ∣ − ∣ A ∩ B ∣ |A \cup B| = |A|+|B|-|A \cap B| ∣A∪B∣=∣A∣+∣B∣−∣A∩B∣
Set A, B and C
∣ A ∪ B ∪ C ∣ = ∣ A ∣ + ∣ B ∣ + ∣ C ∣ − ∣ A ∩ B ∣ − ∣ A ∩ C ∣ − ∣ B ∩ C ∣ + ∣ A ∩ B ∩ C ∣ |A \cup B \cup C| = |A| + |B| + |C| -|A \cap B| - |A \cap C| - |B \cap C| + |A \cap B \cap C| ∣A∪B∪