Equivalence Classes of Diagonal Relation
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Theorem
Let $S$ be a set.
Let $\Delta_S$ denote the diagonal relation on $S$.
The set $\EE_S$ of equivalence classes of $S$ can be expressed as:
- $\EE_S = \set {\set x: x \in S}$
That is, it is the set of all singletons of $S$.
Proof
Let $x \in S$.
Then by definition of the diagonal relation:
- $y \mathrel {\Delta_S} x \iff y = x$
Hence:
- $y \in \eqclass x {\Delta_S} \iff y = x$
That is:
- $\eqclass x {\Delta_S} = \set x$
Hence the result.
$\blacksquare$