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**

![Figure](https://docs.google.com/drawings/d/e/2PACX-1vQV4hFmDdCvL3SvMwvkr6r9QUqr7PsoM8kOkjMvxOWNbTIGCIUaVVGLPTIahe0fGSycwwkfYflegmOD/pub?w=605&h=293)