Henry Ernest Dudeney/Puzzles and Curious Problems/259 - Flies on Window Panes

Puzzles and Curious Problems by Henry Ernest Dudeney: $259$

Flies on Window Panes

The diagram represents a window with $81$ panes.

The dots represent nine flies, on as many panes,

and no fly is in line with another one horizontally, vertically, or diagonally.

Six of those flies are very torpid and do not move,

but each of the remaining three goes to an adjoining pane.

And yet, after this change of station, no fly is in line with another.

Which are the three lively flies, and to which three panes (at present unoccupied), do they pass?

Sources

• 1932: Henry Ernest Dudeney: Puzzles and Curious Problems ... (previous) ... (next): Moving Counter Problems: $259$. -- Flies on Window Panes
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Combinatorial & Topological Problems: Miscellaneous Combinatorial Puzzles: $456$. Flies on Window Panes