Sentence:  Thus we investigate natural T-functions defined on T^T^{\mathbf{D}\otimes A}M to determine all natural operators T\to TT^T^A for \mathbf{D} denoting the algebra of <WSD>dual numbers</WSD>. 
Meaning of the word marked with <WSD> tags:  An element of an algebra (the "algebra of dual numbers") which includes the real numbers and an element &epsilon; which satisfies &epsilon; ≠ 0 and &epsilon;&sup2; = 0.