VALIDATION AND DIFFICULTY
Verified answers.
Difficulty ratings explained.
40 original puzzles across four broad categories. 20 Expert and 20 Extreme. The site also offers 73 game guides and the original PDF.
Validity and difficulty
Validation checks that an answer meets the constraints and, where required, that it is unique or optimal. We rate difficulty based on the techniques and exploration required. We have yet to calibrate these ratings with a panel of solvers.
Expert puzzles combine deductions and case analysis. Extreme puzzles call for deeper chains of reasoning, more interactions or a broader strategic search. The rating considers the work required beyond counting empty cells.
Verification methods by puzzle
SOLO-001 · Classic Sudoku · EXPERT
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 1 intertwined hypotheses, examines 3 states and closes 1 branches by contradiction. The Expert level asks to keep a chain of possibilities in addition to the interactions. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be shorter.
SOLO-002 · Classic Sudoku · EXTREME
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 6 intertwined hypotheses, examines 29 states and closes 14 branches by contradiction. The Extreme level combines eliminations of candidates and deep branched analysis; this is not a ranking based on the number of empty boxes. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be made by the two sides. be shorter.
SOLO-003 · Classic Sudoku · EXPERT
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 1 intertwined hypotheses, examines 3 states and closes 1 branches by contradiction. The Expert level asks to keep a chain of possibilities in addition to the interactions. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be shorter.
SOLO-004 · Classic Sudoku · EXTREME
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 8 intertwined hypotheses, examines 81 states and closes 40 branches by contradiction. The Extreme level combines eliminations of candidates and deep branched analysis; this is not a ranking based on the number of empty boxes. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be made by a single candidate, single places, bare pairs/triples and interactions between units. be shorter.
SOLO-005 · Diagonal Sudoku · EXPERT
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After unique candidates, unique places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 2 intertwined hypotheses, examines 5 states and closes 2 branches by contradiction. The Expert level asks to keep a chain of possibilities in addition to the interactions. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be shorter.
SOLO-006 · Diagonal Sudoku · EXTREME
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 9 intertwined hypotheses, examines 37 states and closes 18 branches by contradiction. The Extreme level combines eliminations of candidates and deep branched analysis; this is not a ranking based on the number of empty boxes. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be made to the extent that it is possible to be shorter.
SOLO-007 · Irregular Sudoku · EXPERT
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 1 intertwined hypotheses, examines 3 states and closes 1 branches by contradiction. The Expert level asks to keep a chain of possibilities in addition to the interactions. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be shorter.
SOLO-008 · Irregular Sudoku · EXTREME
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After single candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 8 intertwined hypotheses, examines 27 states and closes 13 branches by contradiction. The Extreme level combines eliminations of candidates and deep branched analysis; this is not a ranking based on the number of empty boxes. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be made to the extent that it is possible to determine the number of empty boxes. be shorter.
SOLO-009 · Killer Sudoku · EXPERT
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After unique candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive proof reaches 3 intertwined hypotheses, examines 9 states and closes 4 branches by contradiction. The Expert level asks to keep a chain of possibilities in addition to the interactions. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path can be shorter.
SOLO-010 · Killer Sudoku · EXTREME
Exact enumeration, shutdown after two solutions, terminal verification of all units and cages.
After unique candidates, single places, bare pairs/triples and interactions between units, the solver still reaches bifurcations. The exhaustive evidence reaches 9 intertwined hypotheses, examines 127 states and closes 63 branches by contradiction. The Extreme level combines eliminations of candidates and deep branched analysis; this is not a ranking based on the number of empty boxes. Editorial evaluation according to the protocol of the collection, without calibration on a panel of players; another logical path Maybe it's shorter.
SOLO-011 · Advanced Mastermind · EXPERT
Complete listing of all codes; calculation independent of each score; deletion of redundant indices.
The reference method leaves 5 multi set(s) after solving multiplicity constraints; then it is necessary to cross their arrangements with all the position constraints. Repeats prevent the numbers from being treated as a simple set. The reference method combines occurrence counting and configuration removal.
SOLO-012 · Advanced Mastermind · EXPERT
Complete listing of all codes; calculation independent of each score; deletion of redundant indices.
The reference method leaves 1 multi set(s) after solving multiplicity constraints; then it is necessary to cross their arrangements with all position constraints. Repeats prevent treating the numbers as a simple set. The reference method combines occurrence counting and configuration removal.
SOLO-013 · Advanced Mastermind · EXTREME
Complete listing of all codes; calculation independent of each score; deletion of redundant indices.
The reference method leaves 16 multi set(s) after solving multiplicity constraints; then it is necessary to cross their arrangements with all position constraints. The resolution combines equations of multiplicity caps, permutations with repetition and interlocking position constraints. The corrected provides the complete cutting of this exploration. The Extreme level remains an appreciation of this manual effort, without calibration on players.
SOLO-014 · Advanced Mastermind · EXTREME
Complete listing of all codes; calculation independent of each score; deletion of redundant indices.
The reference method leaves 1 multiset(s) after solving multiplicity constraints; then it is necessary to cross their arrangements with all position constraints. The resolution combines equations of multiplicity ceilings, permutations with repetition and intertwined position constraints. The corrected provides the complete cutting of this exploration. The Extreme level remains an appreciation of this manual effort, without calibration on players.
SOLO-015 · Cryptarithm · EXPERT
Complete search by columns, binary deductions, rotation of unallocated numbers and arithmetic control of both equals.
Ten letters and two coupled additions require a combination of retention, injectivity and transport of constraints between equations. A first correct equation leaves several assignments: resolution requires a table of deductions and a systematic exploration, not a simple operation to complete.
SOLO-016 · Cryptarithm · EXPERT
Complete search by columns, binary deductions, rotation of unallocated numbers and arithmetic control of both equals.
Ten letters and two coupled additions require a combination of retention, injectivity and transport of constraints between equations. A first correct equation leaves several assignments: resolution requires a table of deductions and a systematic exploration, not a simple operation to complete.
SOLO-017 · Cryptarithm · EXTREME
Complete search by columns, binary deductions, rotation of unallocated numbers and arithmetic control of both equals.
Ten letters and two coupled additions require a combination of restraints, injectivity and transport of stresses between equations. The large number of surviving substitutions to the first equation makes manual exploration particularly long; the restraint controls must be intertwined in both additions.
SOLO-018 · Futoshiki · EXPERT
Comprehensive research with different domains, constraints, unique locations and inequalities; independent control of the final grid.
The crossover of single lines, single columns and inequities is not closed by propagation of the only forced numbers in the reference solver. The Expert level is based on the combination of single terminals and locations, followed by controlled exploration; it is not only a result of the size of the square.
SOLO-019 · Futoshiki · EXTREME
Comprehensive research with different domains, constraints, unique locations and inequalities; independent control of the final grid.
The crossover of single lines, single columns and inequities is not closed by propagation of the only forced numbers in the reference solver. Entwined hypotheses and non-local contradictions are necessary in its method; this motivates the Extreme level, without pretending to exclude a shorter human trick.
SOLO-020 · Futoshiki · EXTREME
Comprehensive research with different domains, constraints, unique locations and inequalities; independent control of the final grid.
The crossover of single lines, single columns and inequities is not closed by propagation of the only forced numbers in the reference solver. Entwined hypotheses and non-local contradictions are necessary in its method; this motivates the Extreme level, without pretending to exclude a shorter human trick.
SOLO-021 · Nonogram · EXPERT
Enumeration of placements by line, propagation by intersections and exhaustive search for up to two solutions; new verification of response series.
The simple intersection blocks; the crosses require an analysis of nested cases (depth 2, 6 branches impossible in the solver). Editorial level based on this need for coordination, not on the only format of the grid.
SOLO-022 · Nonogram · EXPERT
Enumeration of placements by line, propagation by intersections and exhaustive search for up to two solutions; new verification of response series.
The simple intersection blocks; the crosses require an analysis of nested cases (depth 5, 8 branches impossible in the solver). Editorial level based on this need for coordination, not on the only format of the grid.
SOLO-023 · Nonogram · EXTREME
Enumeration of placements by line, propagation by intersections and exhaustive search for up to two solutions; new verification of response series.
The simple intersection blocks; the crosses require an analysis of nested cases (depth 7, 34 branches impossible in the solver). Editorial level based on this need for coordination, not on the only format of the grid.
SOLO-024 · Nonogram · EXTREME
Enumeration of placements by line, propagation by intersections and exhaustive search for up to two solutions; new verification of response series.
The simple intersection blocks; the crosses require an intertwined case analysis (depth 10, 16 impossible branches in the solver). Editorial level based on this need for coordination, not on the only format of the grid.
SOLO-025 · Hamiltonian path · EXPERT
DFS comprehensive simple paths, with necessary controls of connection, benchmarks, distance and parity; comparison of all solutions up to two.
Coordinate the intervals between markers, the separations of regions and the constraints of parity. The solver must explore 613 prefixes; the level reflects this combined exploration, without automatically absorbing time of calculation and human difficulty.
SOLO-026 · Hamiltonian path · EXPERT
DFS comprehensive simple paths, with necessary controls of connection, benchmarks, distance and parity; comparison of all solutions up to two.
Coordinate the intervals between markers, the separations of regions and the constraints of parity. The solver must explore 423 prefixes; the level reflects this combined exploration, without automatically absorbing time of calculation and human difficulty.
SOLO-027 · Hamiltonian path · EXTREME
DFS comprehensive simple paths, with necessary controls of connection, benchmarks, distance and parity; comparison of all solutions up to two.
Coordinate the intervals between markers, the separations of regions and the constraints of parity. The solver must explore 5682 prefixes; the level reflects this combined exploration, without automatically absorbing time of calculation and human difficulty.
SOLO-028 · Pentomino tiling · EXPERT
Accurate coverage of boxes and coin identities, all free orientations; counting up to two solutions and independent verification of groups of five boxes.
Combining orientations, constraints of indices and impossibility of coverage; 980 sub-pavements are examined with choice of the most constrained box. The level is editorial and does not rely on an external standard.
SOLO-029 · Pentomino tiling · EXTREME
Accurate coverage of boxes and coin identities, all free orientations; counting up to two solutions and independent verification of groups of five boxes.
Combining orientations, constraints of indices and impossibility of coverage; 6105 sub-pavements are examined with choice of the most constrained box. The level is editorial and does not rely on an external standard.
SOLO-030 · Pentomino tiling · EXTREME
Accurate coverage of boxes and coin identities, all free orientations; counting up to two solutions and independent verification of groups of five boxes.
Combining orientations, constraints of indices and impossibility of coverage; 13455 sub-pavements are examined with choice of the most constrained box. The level is editorial and does not rely on an external standard.
SOLO-031 · Othello / Reversi · EXPERT
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
Several first moves are legal; an estimate by the immediate gain does not replace the calculation until the end. The resolution requires a minimum tree on several floors, with verification of the turns and mobility. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-032 · Othello / Reversi · EXPERT
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
Several first moves are legal; an estimate by the immediate gain does not replace the calculation until the end. The resolution requires a minimum tree on several floors, with verification of the turns and mobility. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-033 · Othello / Reversi · EXPERT
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
Several first moves are legal; an estimate by the immediate gain does not replace the calculation until the end. The resolution requires a minimum tree on several floors, with verification of the turns and mobility. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-034 · Othello / Reversi · EXTREME
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
End of part requiring a ramified defense shaft on ten or eleven boxes, with possible beating orders, mobility and passes. It is necessary to combine retrograde calculation, control of adverse responses and exact comparison of alternatives; no local corner or immediate majority rule is sufficient. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-035 · Othello / Reversi · EXTREME
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
End of part requiring a ramified defense shaft on ten or eleven boxes, with possible beating orders, mobility and passes. It is necessary to combine retrograde calculation, control of adverse responses and exact comparison of alternatives; no local corner or immediate majority rule is sufficient. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-036 · Othello / Reversi · EXTREME
Legal part generation from the standard initial position; exhaustive minima stored to the end, without truncated depth or leaf heuristic. All the values of the first strokes are checked.
End of part requiring a ramified defense shaft on ten or eleven boxes, with possible beating orders, mobility and passes. It is necessary to combine retrograde calculation, control of adverse responses and exact comparison of alternatives; no local corner or immediate majority rule is sufficient. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-037 · Nim — pair subtraction · EXPERT
Accurate dynamic programming of Grundy numbers, control of the mex and all the first moves. The sum property is demonstrated in the fix.
Combine mex recurrence and XOR sum of non-standard games; demonstrate a valid strategy for all responses. Sizes do not treat like those of the ordinary Nim. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-038 · Nim — pair subtraction · EXPERT
Accurate dynamic programming of Grundy numbers, control of the mex and all the first moves. The sum property is demonstrated in the fix.
Combine mex recurrence and XOR sum of non-standard games; demonstrate a valid strategy for all responses. Sizes do not treat like those of the ordinary Nim. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-039 · Nim — pair subtraction · EXTREME
Accurate dynamic programming of Grundy numbers, control of the mex and all the first moves. The sum property is demonstrated in the fix.
Build a Grundy table with two variables, assemble three components by XOR, list all the winning hits and prove the universal answer. The difficulty is on several combined tools, not on a long calculation of isolated chips. Editorial evaluation based on the required techniques; not calibrated by a human panel.
SOLO-040 · Nim — pair subtraction · EXTREME
Accurate dynamic programming of Grundy numbers, control of the mex and all the first moves. The sum property is demonstrated in the fix.
Build a Grundy table with two variables, assemble three components by XOR, list all the winning hits and prove the universal answer. The difficulty is on several combined tools, not on a long calculation of isolated chips. Editorial evaluation based on the required techniques; not calibrated by a human panel.
Limits
Search statistics depend on the order of exploration. A human solver may find a shorter proof. Each combinatorial variant follows the rules given with its puzzle. Tactical solutions apply to the exact position and scoring rules stated in the puzzle.