ABSTRACT
The addition principle could be restated as follows: if X and Y are two disjoint sets then | X ∪ Y | = | X | + | Y | . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315366890/f4bfe916-bec8-4e54-8a5a-ffef17c80cb7/content/eq209.tif"/>
