### Theory:

• Tertrominoes are observed (or) assumed as if they are fixed into only being in "Orthogonal" rotations.
• "Orthogonal" refers to being lined up with the horizontal and vertical axes.
Properties:
• Mirror symmetry can occur only along $$2$$ axes.
• Reflection along the horizontal axes is called the $$X$$-Reflection.
• Reflection along the vertical axes is called the $$Y$$-Reflection.
• Every tetromino can have $$1$$ of $$4$$ possible symmetries. ("Symmetric with $$Y$$" (or) "Symmetric with $$X$$" (or) "Symmetric to both" (or) "Asymmetric").