Finned X-Wing: keep the fish and account for the fin
A finned X-Wing is an X-Wing with an extra base candidate outside the two cover columns.
Key idea
If the fin is false, the X-Wing works; if the fin is true, it eliminates nearby peers. Only targets covered by both cases are safe.
See the move, step by step
Use the extra 7 at R1C2 as the fin.
Step 1 of 4
Find a near X-Wing
Rows 1 and 3 nearly form an X-Wing on columns 1 and 3, but row 1 has one extra 7.
Step 2 of 4
Separate fish cells from the fin
The four corners form the fish; R1C2 is the fin inside box 1.
Step 3 of 4
Keep only the shared elimination
R2C3 sees the fin and also lies in a cover column. Both possible cases eliminate its 7.
Step 4 of 4
Do not clear the whole column
Only R2C3 is justified here. The fin prevents the unrestricted X-Wing cleanup farther away.
Try it on today's puzzle
Treat a fin as a conditional branch. Eliminate only candidates that both see every fin and would be removed by the finless fish.
Play today