数独中的X翼是什么？

X-Wing applies to a specific digit when it appears as a candidate in exactly two cells in one row, and those two cells are in the same two columns as exactly two candidates for the same digit in another row. The four candidate cells form the corners of a rectangle - The shape that gives the technique its name.

如果数字D只能放在行R1中的列C1和C2中，那么D必须占据这两个单元格之一。同样适用于行R2。两行一起将把D放在列C1和C2中——各一个，以某种顺序。这意味着D不能出现在列C1或C2中的任何其他地方。从这两列的所有其他单元格中移除它。

数字6在第2行中恰好是两个单元格的候选数：第3列和第7列。数字6在第8行中也恰好是两个单元格的候选数：第3列和第7列。这四个单元格在R2C3、R2C7、R8C3、R8C7形成角点。

无论解如何在第2行和第8行分配6，第3列将在其中一行得到6，第7列将在另一行得到6。因此从第3列和第7列的所有其他单元格中消除6。

The pattern works starting from columns too. If digit D appears as a candidate in exactly two cells in column C1, and those cells share the same two rows as exactly two candidates for D in column C2, eliminate D from all other cells in those two rows. Same logic, same result, different orientation.

剑鱼将X翼扩展到三行（或三列）。除此之外还有水母（四行/列）、XY翼和多步链。X翼是整个高级模式家族的入门点——先掌握它。