Picture sudoku · the one rule
One of
each
in every row.
🐱
🐶
🐸
🐰
🐸
🐰
🐱
🐶
🐰
🐸
🐶
🐱
🐶
🐱
🐰
🐸
The one rule
↔
Each row has one of each animal — no repeats
↕
Each column has one of each — no repeats
⊞
Each little box has one of each — no repeats