D. If, = a(t ? h), h ? R + , denotes the ring of differential time-delay operators with polynomial coefficients in t, then Kdim(D) = 2. More generally, if D = A 1 (k), h i ? R + , and the Q-vector space formed by the h i is n-dimensional, then Kdim(D) = n + 1

D. If, [? n ; ? n , ? n ] denotes the algebra of forward shifts with rational coefficients, where ? i and ? i are defined by ? i (a)(x 1 , . . . , x n ) = a(x 1 , . . . , x i?1 , x i + 1, x i+1

D. If, ? 1 ; ? 1 , ? 1 ] . . . [? n ; ? n , ? n ] denotes the algebra of forward shifts with polynomial coefficients, where ? i and ? i are defined as in 4

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