A pseudoscalar is invariant under proper rotations but changes sign under a spatial reflection. In three dimensions the scalar triple product is a pseudoscalar.
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A pseudoscalar is a quantity that transforms like a scalar under proper Lorentz transformations but gains an additional minus sign under improper transformations, such as parity transformations (spatial inversion). This means that while a pseudoscalar remains unchanged under rotations and boosts (proper transformations), it changes sign when the spatial coordinates are inverted.