Summo: "You are not able to determine the sum S."

-> this sum has no associated product that uniquely determines x and y
-> sum is 11, 17 or 23

11 ( 4):                                                  30 28 24 18 (min=2,max=3)
17 ( 7):                                72 70 66 60 52 42 30 (min=2,max=5)
23 (10):  132 130 126 120 112 102 90 76          60    42 (min=2,max=6)

Prodo says:

product is: 30, 42 or 60

30 ( 3):  11 13 17 (min=4,max=7)
42 ( 3):  13 17 23 (min=5,max=10)
60 ( 5):  16 17 19 23 32 (min=7,max=15)

Summo says: sum = 11