This is partly described in the text. In addition, it illustrates:
rules Sales(Prod1, 2019) = Sales(Prod1, 2017) + Sales(Prod1, 2018)
rules Sales(Prod2, 2019) = Sales(Prod2, 2017) + Sales(Prod2, 2018)
Then the output of the MODEL clause:
country values of A, A, A, A, B, B, B, B as original data product values of Prod1, Prod1, Prod1, Prod2, Prod1, Prod1, Prod2, Prod2, as original data
year values of 2017, 2018, 2017, 2018, 2017, 2018, 2017, 2018 as original data
sales values of 10, 15, 12, 16, 21, 23, 28, 29 as original data
country values as rule results A, A, B, B
product values as rule results Prod1, Prod2, Prod1, Prod2
year values as rule results 2019, 2019, 2019, 2019
sales values as rule results 25, 28, 44, 57