If 1 = Single, 2 = Double, 3 = Triple, 4 = Quadruple, what are 5, 6, 7, 8, etc. called?
Why does the matrix [math] M = \begin{bmatrix}1 & 2  & 3\\4 & 5 & 6\\7 & 8 & 9\end{bmatrix} [/math] have a [math]0[/math] determinant?