Alfaelo

What is Alfaelo

Alfaelo is a nine-by-nine sudoku played with letters instead of numbers. Each puzzle uses a fixed set of nine letters, shown on the alphabet strip above the grid. You place them so that every row, every column and every three-by-three box holds all nine letters exactly once. Given letters are printed in grey and cannot be changed; your own entries appear in blue. When the grid is full and correct, the clock stops and the round is scored.

What makes Alfaelo different is the blue dots between cells. A dot means the two letters it separates are next to each other in the alphabet, D and E for instance. The rule cuts both ways: where two touching cells have no dot between them, those letters are not alphabet neighbours. That second half is where most of the solving happens. An empty edge looks like nothing at all, yet it quietly removes candidates, which is why a hard grid with only five given letters still has a single solution.

How to play

1. Choose a level, then read the alphabet strip at the top. The highlighted letters are the nine in play and the arcs show which pairs are consecutive.
2. Tap a letter on the keypad to select it, then tap an empty cell to place it. Tapping a filled cell highlights every copy of that letter, and backspace clears the selected cell. The arrow keys and typing a letter work too.
3. Use the dots while you fill. A dot between two cells means those letters are one step apart in the alphabet; an edge with no dot means they are not.
4. Press Check whenever you want the board tested: wrong cells turn red. Complete the grid with no errors and the round ends, the timer stops and you can enter a name for the ranking.

Strategies that work

• Start with the alphabet strip. Only some of the nine letters have a partner one step away, and those are the only letters a dot can ever join. A letter with no neighbour in the set can never sit on a dotted edge, so you can strike it from every dotted pair straight away.
• Letters at the end of a chain are the most useful. If the set holds D, E and F, a dotted edge beside a cell containing E may be D or F, but a dotted edge beside D must be E.
• Read the empty edges as clues. Whenever a candidate would create an alphabet pair across an undotted edge, discard it. On the hard grids this negative information does more work than the given letters do.
• Use the highlighting. Selecting a letter shades every row, column and box that already contains it, so the pale cells left over are the only places it can still go. Sweeping one letter at a time beats staring at one empty cell.
• Check sparingly. Each press of Check costs 15 points and each wrong cell it finds costs 25, so testing a half-finished grid is expensive. A careful minute costs less than one bad Check.

A little history

Alfaelo is an original puzzle rather than a traditional one, though every piece of it has a long record. A grid where each symbol appears once per row and column is a Latin square, a structure studied formally by Leonhard Euler in the eighteenth century; sudoku adds the box condition on top. The modern puzzle was published as Number Place in Dell magazines in 1979 and was popularised in Japan by the publisher Nikoli in the mid-1980s under the name sudoku. Because it only needs nine distinguishable symbols, letters work exactly as well as digits: the numerals never carry arithmetic meaning. Dot variants are equally well established, with consecutive sudoku and Kropki sudoku marking relationships between touching cells and relying on the convention that an unmarked edge denies the relationship. Alfaelo joins the two ideas, so the dots point to alphabetical order instead of numerical order.

Frequently asked questions