Platon Sudoku · Sudoku Study
Fish cover lines · Core Concepts
Cover lines are the crossing rows or columns containing all same-digit candidates from the bases. Here the 2s from blue rows lie in amber columns; a basic fish has equally many bases and covers.
This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.
View on Google PlayDefinition
Cover lines are the crossing rows or columns containing all same-digit candidates from the bases. Here the 2s from blue rows lie in amber columns; a basic fish has equally many bases and covers.
How to find it
Find every 2 on the blue lines, then count the amber lines: two bases need two covers, three need three.
Common mistake
Four corners are not enough. An extra 2 outside the covers breaks the basic fish condition.
X-Wing · Row
Teaching board · local candidate diagram
Observe candidates
Look only at candidate 2, at r2c2, r2c8, r6c2, r6c8; the line names can wait.
Verify the condition
Start from the blue row 2, row 6 and find every 2; each line must eventually contain one 2. These selected starting lines are the bases.
Draw the conclusion
Every 2 on row 2, row 6 lies in the amber column 2, column 8; there are 2 bases and as many covers.
X-Wing · Column
Teaching board · local candidate diagram
Observe candidates
Look only at candidate 2, at r2c2, r8c2, r2c6, r8c6; the line names can wait.
Verify the condition
Start from the blue column 2, column 6 and find every 2; each line must eventually contain one 2. These selected starting lines are the bases.
Draw the conclusion
Every 2 on column 2, column 6 lies in the amber row 2, row 8; there are 2 bases and as many covers.
Swordfish · Row
Teaching board · local candidate diagram
Observe candidates
Look only at candidate 2, at r2c2, r2c5, r5c5, r5c8, r8c2, r8c8; the line names can wait.
Verify the condition
Start from the blue row 2, row 5, row 8 and find every 2; each line must eventually contain one 2. These selected starting lines are the bases.
Draw the conclusion
Every 2 on row 2, row 5, row 8 lies in the amber column 2, column 5, column 8; there are 3 bases and as many covers.
Swordfish · Column
Teaching board · local candidate diagram
Observe candidates
Look only at candidate 2, at r2c2, r5c2, r5c5, r8c5, r2c8, r8c8; the line names can wait.
Verify the condition
Start from the blue column 2, column 5, column 8 and find every 2; each line must eventually contain one 2. These selected starting lines are the bases.
Draw the conclusion
Every 2 on column 2, column 5, column 8 lies in the amber row 2, row 5, row 8; there are 3 bases and as many covers.
Recognition practice
Teaching board · local candidate diagram
Recognition practice 1
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 2
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Recognition practice 3
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 4
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Recognition practice 5
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 6
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Recognition practice 7
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 8
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Recognition practice 9
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 10
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Recognition practice 11
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
Yes
Recognition practice 12
Do the amber cover lines contain every candidate on the blue bases?
Draw the conclusion
No
Practice
This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.
View on Google Play