Maestro n° 103 : Page 78 - Gr 75
r2c3 -3- r4c3 =3=9= r4c3 -9- r4c5 =9= r9c5 -9-7- r9c5 =7= r1c5 -7- r1c1 =7= r2c3 => r2c3 ≠ 3