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$\underline{Def}$
Let $A \in M_{n \times n}$.
Define $A^{1}=A,\, A^{2}= A^{1} \cdot A.$
Define recursively that $A^{k}=A^{k-1} \cdot A$ $\forall \geq 2$.
Define $A^{0}=I_{n}$.
$\underline{Ex}$
$A=\begin{bmatrix} 0 & 0 \\ 1 & 0 \end{bmatrix},\; A^{2}=0$.
Cancellation law does not hold for matrix product.
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