German Whispers

German whisper is line marked with red. Neighboring digits on German whisper line must differ by 5. German whisper line cannot contain 5 because we would have to use 0 or 10 as neighbor next to 5, which means values on the line must alternate between low digits (1, 2, 3, 4) and high digits (6, 7, 8, 9).

In the right box on the image above we can conclude that yellow cell is 1 because we have 3 cells on German whisper line, which means we have one low digit and two high digits or one high digit and two low digits. In this case only one low digit is available, which meas cell in between must be low digit and other two must be high digits.

Numbers 6 and 4 are sometimes restricted. When a cell has two neighboring cells which are in same house (row, column or box) that cell cannot be 6 or 4, because both neighboring cells would have to be 1 or 9. That means in case when German whisper line is in single house only edge cells can be 6 or 4.

In case when cell has neighboring cells which are not sharing a house those cells can be 4 or 6.