Edit: OK it took me a while but here's why.
The maximum distance allowed between 17th and 16th place must be 5 or less points. Currently, the team in 17th place is Cosenza on 35 (-7 points off Pordenone in 16th). Reggiana are 18th on 34.
The last game of the season sees Pordenone and Potenza squaring off so they can't both lose and therefore Reggiana can't mathematically make it anymore.
Assuming Reggiana wins their next game and go to 37 points:
-if Pordenone wins, they will still be +8points.
-in case of a draw, Pordenone will be +6 points
-if Cosenza wins they will still be +1 on Reggiana and will keep their play out spot and thus send Reggiana down.
The maximum distance allowed between 17th and 16th place must be 5 or less points. Currently, the team in 17th place is Cosenza on 35 (-7 points off Pordenone in 16th). Reggiana are 18th on 34.
The last game of the season sees Pordenone and Potenza squaring off so they can't both lose and therefore Reggiana can't mathematically make it anymore.
Assuming Reggiana wins their next game and go to 37 points:
-if Pordenone wins, they will still be +8points.
-in case of a draw, Pordenone will be +6 points
-if Cosenza wins they will still be +1 on Reggiana and will keep their play out spot and thus send Reggiana down.