\begin{definition}[Definition:Orientation of Coordinate Axes/Cartesian Plane/Left-Handed]
A Cartesian plane is defined as being '''left-handed''' if it has the following property:
Let a '''left hand''' be placed, with palm uppermost, such that the thumb points along the $x$-axis in the positive direction, such that the thumb and index finger are at right-angles to each other.
Then the index finger is pointed along the $y$-axis in the positive direction.
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\end{definition}