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[[[>50 This page needs revisiting - it's _ rather technical, and unclear as _ to why it's a useful concept. ]]]

A Binary Relation * defined on a set A is defined as the set of all ordered pairs (a, b) of elements of A with the property that a * b.

Consider the set B = { Albert Einstein, Queen Victoria, David Beckham, Florence Nightingale } and the relation "is the same gender as".

Then Albert Einstein * David Beckham and David Beckham * Albert Einstein. Similarly Albert Einstein * Albert Einstein !!!

A further example, consider EQN:Z , the set of integers. The relation "is greater than" would define such ordered pairs as ( 7, 4) and (-6, -12).

Question: Which person in the set B developed a type of pie chart? Clue: It wasn't Albert Einstein.