Sudoku N

[koala]

Please, what does the "N=7" mean?
As it cannot be the rules of the consecutive-7, I don´t understand the rules of this week´s "Tough only".

Best wishes,
Koala

[gabriele]

https://www.argio-logic.net/forum/viewtopic.php?f=68&t=6636

The idea comes from the "No Four" of next french contest "L’ALPHABET DU NO"

Place numbers in the grid such that every row, column and 3x3 box contain the numbers 1 to 9. if Any operation (+,-,*,/) performed between two orthogonally adjacent cells leads to a result of N, then the two cells are separated by a blu line. The dark rules applies: if there is no line the result can not be N

[koala]

Thank you very much for your help!
Koala