1.3 - Determination of subset $I$

If $k\leq\frac{N}{3}$ then $I=\{1,4,7,10\}$ If $\frac{N}{3}\leq k \geq\frac{2N}{3}$ then $I=\{1,2,4,5,7,8,10,11\}$ If $\frac{N}{3+1}\leq k$ then $I=\{1,2,3,...12\}$ Finally, the new series $S' = \{r'_1;...r'_{12}\}$ is calculated in base of the following rule:

$${r'_{i}} = \left\{\begin{array}{ccccc} r_{i} & if & i \notin I\... ... l > k\\ \\ r_{i} - O & if & i \in I & and & l < k\\ \end{array}\right.$$

The series is finally recombined in base to one of the counterpoint combinations that the program apply automatically during the score generation process. This combinations are: retrogradazione a croce (nine combinations) retrogrado (one combinations) slittamento (eleven combinations)