Symmetry Place

Rules

Enter a letter A or B or C into some cells of the diagram. The symbols in each row and each column must form a palindrome. (A palindrome is a sequence of symbols that is the same when viewed from the front and back, for example, ABCCBA or BCACB).

(Rules and example (modified) from janko.at[1])

Rule variations

• Palindrome from WPC 2017 introduced two additional rules: (1) no two blank cells share an edge, (2) each row/column contain at least two different letters. This idea comes from Rajesh Kumar (India), most likely independently of Symmetry Place.[2][3]

History of the puzzle

Invented by Naoki Inaba (Japan) in 2000.[4] Original title シンメトリープレース is a transliteration of English "Symmetry Place". However, due to the simplicity of the rules, this puzzle was reinvented multiple times.

Variants

Palindrome^2

Invented by Deb Mohanty (India). First appeared on WPC 2017/Round 20.

Place a letter A or B or C in some of the cells. Some cells will remain blank, but blank cells do not share an edge. Each row and each column of the grid, and each row and each column of the thickly outlined square regions within the grid, form palindromes. A palindrome has at least 2 different letters and reads the same from both sides, ignoring the blank cells.