Eulero, also known as a Graeco-Latin Square or Euler Square, is a fascinating logic puzzle that combines elements of Latin squares and Sudoku. Here’s what a small puzzle looks like:
The puzzle is played on a square grid. Bigger grids mean harder puzzles. Each cell in the grid must contain one letter and one digit. Normally, the letters and digits corresponds to the size of the grid. So in a 5x5 grid, we use use the letters A to E and the digits 1 to 5.
The objective of Eulero is to fill out the grid such that every row and every column contains each letter and each digit exactly once - ie no row or column can have a repeated letter or digit. Additionally, no two cells in the grid can contain the same pairing of a letter and a digit.
Here’s what our example puzzle looks like when complete:
Start with Known Pairs. Some cells are already filled in, or are partially filled in (depending on the difficulty level of the puzzle), so use them as a starting point. The given pairs can help you determine what can't be in the same row or column.
Elimination. If you're unsure about where a particular symbol should go, consider where it can't go. This process of elimination can narrow down your options.
Sudoku. Eulero follows similar rules to Sudoku, which means that many Sudoku techniques can either be used directly, or adapted, to help solve the puzzle. See our detailed three-part Sudoku tutorial here for some ideas.
Fancy filling some thermometers? We publish this puzzle occasionally in our free Puzzle Weekly magazine. You should totally sign up for that if you haven’t already, as it puts 28 brand new puzzles in your inbox every week.
You can also find lots of Thermometers puzzles in our Jumbo Adult Puzzle Book – which happens to include more than 500 puzzles of 20 different varieties.