Finned X-Wing

Overview

A Finned X-Wing is an X-Wing with one or two extra candidates, the fin, in one of its rows, inside the box of one corner. The digit still goes from the cells that both the X-Wing and the fin rule out.

How It Works

Take a digit with exactly two places in one row and, in a second row, places in the same two columns plus a fin: one or two extra cells in the same box as one of the corners. If the fin doesn't hold the digit, the four corners are an X-Wing and the digit goes from the rest of both columns. If the fin holds it, the digit goes from the rest of the fin's box. One of the two is true, so the digit goes from cells that are in one of the two columns and also in the fin's box, apart from the corners themselves. The same works with rows and columns swapped, and even when the corner inside the fin's box is missing (a sashimi X-Wing).

When To Use It

Look for a Finned X-Wing when a digit almost makes an X-Wing: two rows (or columns) line up, but one of them has an extra place or two in the same box as a corner.

How To Detect It

For a digit, find a row with exactly two places. Find another row whose places are in the same two columns, plus extra places that all sit in one box with one of the corners: the fin. That corner may even be missing (a sashimi X-Wing). Remove the digit from cells in those two columns that are inside the fin's box, apart from the corners themselves.

Visual Example