Using the Hodge star operator ⋆ ⋆ , the exterior derivative d is related to the codifferential through δ δ = − − ⋆ ⋆ d ⋆ ⋆ . These form the Laplace–de Rham operator d − − δ δ which can be viewed as the square root of the Laplacian operator since ( d − − δ δ ) 2 = ◻ ◻ . The Dirac–Kähler equation is motivated by noting that this is also the property of the Dirac operator, yielding