- 166 -Mazzola, Guerino / Noll, Thomas / Lluis-Puebla, Emilio: Perspectives in Mathematical and Computational Music Theory 
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In order to determine the number of Vuza constructible canons of length 144 with |L|= 12 , we first realize that Vuza’s algorithm yields 6 different sets L and 36 different possibilities for A , which also consists of 12 elements. So, when exchanging the role of L and A , we have to take care to count only non-isomorphic canons. As a matter of fact, here in this case the process of exchanging L and A yields new canons, so that in addition to the previous 216 canons (L,A) we have another 216 canons of the form (A,L) . Hence, we end up with 432 Vuza constructible canons of length 144 with |L |= |A |= 12 . Moreover, there exist 8424 Vuza constructible canons with |L|= 6 and 8424 Vuza constructible canons with |L |= 24 , so that in conclusion there are 17280 Vuza constructible canons of length 144 .

Finally, we want to deal with the question whether there exist regular complementary canons of maximal category which are not Vuza constructible canons. In Fripertinger (2002) for an integer d > 1 we introduced the function yd defined on {0,1} such that yd(0) is the vector (0,0,...,0) consisting of d entries of 0 , and yd(1) = (0,...,0,1) is a vector consisting of d- 1 entries of 0 and 1 in the last position. We write the values of yd in the form

 d d- 1 yd(0) = 0 , yd(1) = 0 1.

If we apply yd to each component of a vector  Zn f (- {0,1} we get a vector  Znd yd(f) (- {0,1} by concatenating all the vectors yd(f (0)),...,yd(f(n- 1)) . Among other properties we showed that

  1. f0 (- {0,1}Zn is the canonical representative of Cn(f ) if and only if yd(f0) is the canonical representative of Cnd(yd(f)) .
  2. f /= 0 is acyclic if and only if yd(f) is acyclic.

The mapping yd can be considered as an augmentation, mapping a rhythm in Zn to an augmented rhythm in Znd . In correspondence with yd , we define the mapping Yd which can be interpreted as k -fold subdivision. It also maps a rhythm in Zn to a rhythm in Znd . It is defined on {0,1} by

 d d Yd(0) = 0 , Yd(1) = 1 .

Again the value Yd(f) for  Zn f (- {0,1} is obtained by concatenation of the vectors Yd(f(0)),...,Yd(f (n - 1)) . It is easy to prove that the mapping Yd satisfies


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- 166 -Mazzola, Guerino / Noll, Thomas / Lluis-Puebla, Emilio: Perspectives in Mathematical and Computational Music Theory