Doppelblock

Doppelblock is a Japanese logic puzzle where solvers shade two cells in each row and column of a grid. The unshaded cells must contain numbers that satisfy Latin square constraints (no repetition in any row or column) while also matching the clue numbers provided outside the grid, which typically indicate the sum of values between the two shaded blocks. Created by Japanese puzzle designer Naoki Inaba, Doppelblock combines elements of Latin square puzzles with computational constraints, requiring both logical deduction and basic arithmetic. The puzzle appeals to logic enthusiasts who enjoy number-placement challenges with additional structural constraints.