\begin{definition}[Definition:Simson Line]
Let $\triangle ABC$ be a triangle.
Let $P$ be a point on the circumcircle of $\triangle ABC$.
Construct perpendiculars from $P$ to each of the sides of $\triangle ABC$.
Let $D$, $E$ and $F$ be the feet of those perpendiculars.
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The line $DEF$ called the '''Simson line'''.
\end{definition}