PDF

or solve online (using our beta test of Penpa-Edit tools)

Theme: Open Middle

Author/Opus: This is the 550th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF. (We are not sharing time standards but are interested in seeing some reported times as well as solution animations from solvers on the Discord.)

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.