Binary operation : Composition is a binary operation. That is, a ∘ ∘ b is a symmetry for any two symmetries a and ⁠ b ⁠. For example, r 3 ∘ ∘ f h = f c , that is, rotating 270° clockwise after reflecting horizontally equals reflecting along the counter-diagonal (⁠ f c ⁠). Indeed, every other combination of two symmetries still gives a symmetry, as can be checked using the Cayley table.