Partition Equation

Theorem
Let group $G$ act on a finite set $X$.

Let the distinct orbits of $X$ under the action of $G$ be:
 * $\Orb {x_1}, \Orb {x_2}, \ldots, \Orb {x_s}$

Then:
 * $\card X = \card {\Orb {x_1} } + \card {\Orb {x_2} } + \cdots + \card {\Orb {x_s} }$

Proof
Follows trivially from the fact that the Group Action Induces Equivalence Relation.