 However, though as multivectors rotors also transform double-sidedly, rotors can be combined and form a group, and so multiple rotors compose single-sidedly.The alternative formulation above is not self-normalizing and motivates the definition of spinor in geometric algebra as an object that transforms single-sidedly – i.e.spinors may be regarded as non-normalised rotors in which the reverse rather than the inverse is used in the sandwich product.