Count the number of non-ID columns in Eq. (3.1).
Count the number of arrows in Eq. (3.2).
They should be the same number; is this a coincidence?

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**Equation 3.1**

$\begin{array}{c|ccc} Employee & FName & WorksIn & Mngr \\\\ \hline 1 & Alan & 101 & 2 \\\\ 2 & Ruth & 101 & 2 \\\\ 3 & Kris & 102 & 3 \end{array}$

$\begin{array}{c|cc} Department & FName & WorksIn & Mngr \\\\ \hline 101 & Sales & 1 \\\\ 102 & IT & 3 \end{array}$

**Equation 3.2**