TUVWXYZ-Wing
A TUVWXYZ-Wing is the largest ALS-Wing: six almost-locked-set cells and a bivalue pivot linked through a single restricted common. The pivot's non-restricted candidate becomes impossible across all seven cells, so it can be eliminated from any external cell that sees every Wing cell holding it.
What is a TUVWXYZ-Wing?
A TUVWXYZ-Wing extends the UVWXYZ-Wing from six cells to seven. The pattern consists of a bivalue pivot cell and six almost-locked-set cells, linked through a single restricted common — one of the pivot's two candidates. The six ALS cells collectively hold seven candidates for six cells, and the restricted common ties them to the pivot. If the pivot's other candidate were true, it would be removed from all six ALS cells (they see the pivot), leaving only five candidates for six cells — a contradiction. The double-linked counterpart is the TUVWXYZ-Ring, where both pivot candidates are restricted commons and the seven cells form a locked set.
How to spot it
Start from a bivalue cell — the pivot — and look for six cells that all see the pivot and whose combined candidates include the restricted common plus at least five extras. The restricted common must appear in at least two ALS cells that see each other, so it is locked within the set. The six cells form an almost-locked set with seven candidates for six cells, and the single restricted common links them to the pivot. TUVWXYZ-Wings are among the rarest patterns in Sudoku and appear only in the most diabolical puzzles once every smaller ALS pattern has been exhausted.
The logic
The pivot has two candidates, say X and Y, where X is the restricted common. If the pivot were Y, then Y would be removed from all six ALS cells (they see the pivot), and the ALS would have only five candidates left for six cells — impossible. So the pivot cannot be Y, and Y can be eliminated from any external cell that shares a house with all Wing cells containing Y. The seven cells never actually form a locked set (unlike the Ring variant); the elimination follows from the contradiction that Y creates in the ALS.