Why the Caged Bird Whispers
A collection of constraints with interesting interactions. We started this puzzle and set it aside for a while, finally adding an extra clue to make it more fun. This puzzle also appears in the Heartburn Collection.
Estimated difficulty: 3.5/5
Rules
Normal sudoku rules apply. Each row, column, and box must contain a complete set of the digits 1-9.
Normal killer cage rules apply: digits in cages cannot repeat and must sum to the number shown in the upper left corner of the cage.
Digits along a thermometer must strictly increase from bulb to top but do not have to be consecutive.
Green lines are German whispers lines. Adjacent digits along the line must differ by 5 or more.
Purple lines are Renban lines. Digits along a renban line form a set of consecutive digits in any order.
Modular X-Sums
A precursor to Residual X-Rays, this puzzle was our first set using hidden modular lines. It also appears in the Heartburn Collection.
Estimated difficulty: 3/5
Rules
Normal sudoku rules apply. Each row, column, and box must contain a complete set of the digits 1-9.
X-Sums: Digits outside the grid give the total of the first X digits in row or column, where X is the first digit along that row or column, starting with value outside the grid.
Every X-sum forms a hidden modular line of length X.
Modular lines: Every set of three sequential digits along a modular line must contain a complete set of residues modulo 3, i.e. one digit from {1,4,7}, one from {2,5,8}, and one from {3,6,9}.
