According to the equivalence relation R, the elements in the set a = {1, 2,3,4} are grouped into a group {1} and {2,3,4} are equivalent classes composed of R Remarks: {1} ∩ {2,3,4.

Putting an equivalent class in curly braces {{ 1}, {2,3,4}} is the equivalent division of A.

Equivalence relation is the union of Cartesian products of elements in the equivalence division, that is

r =({ 1 }×{ 1 })∨( { 2，3，4}×{2，3，4})

={,,,,,,,,,}。

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