A coin is placed on each of the $13$ squares in the following diagram:

Each coin may be showing heads or tails arbitrarily. An adversary points to a square in the $3\times 3$ grid. You must communicate this position to your ally, by flipping precisely $1$ coin.

Standard Devil's Chessboard rules apply:

1. The arrow is there to unambiguously label all the squares.
2. Every coin has a head on one side and a tail on the other.
3. You must flip a coin.
4. You and your ally are shown the diagram and have the problem explained to you in advance. You may then agree a strategy beforehand. The only things you do not know in advance are which coins are showing heads and which are showing tails, and the square which needs to be communicated.
5. Your ally has to deduce the position of the square, only from looking at the diagram with its configuration of coins showing heads and tails, after you made your flip.

No knowledge of the original Devil's Chessboard problem or solution is required.

Motivation The solution to the original Devil's Chessboard problem allows you to communicate a number between $1$ and $n$ with $m$ coins whenever $n\leq 2^k\leq m$, for an integer $k$. It is also well known that there is no solution when $n=m$ unless $n=2^k$. This frequently leads people to conjecture that there is only a solution if $n\leq 2^k\leq m$. This elementary puzzle disproves that conjecture, as there are no powers of $2$ between $9$ and $13$.

A coin is placed on each of the $13$ squares in the following diagram:

Each coin may be showing heads or tails arbitrarily. An adversary points to a square in the $3\times 3$ grid. You must communicate this position to your ally, by flipping precisely $1$ coin.

Standard Devil's Chessboard rules apply:

1. The arrow is there to unambiguously label all the squares.
2. Every coin has a head on one side and a tail on the other.
3. You must flip a coin.
4. You and your ally are shown the diagram and have the problem explained to you in advance. You may then agree a strategy beforehand. The only things you do not know in advance are which coins are showing heads and which are showing tails, and the square which needs to be communicated.
5. Your ally has to deduce the position of the square, only from looking at the diagram with its configuration of coins showing heads and tails, after you made your flip.

No knowledge of the original Devil's Chessboard problem or solution is required.

Motivation The solution to the original Devil's Chessboard problem allows you to communicate a number between $1$ and $n$ with $m$ coins whenever $n\leq 2^k\leq m$, for an integer $k$. It is also well known that there is no solution when $n=m$ unless $n=2^k$. This frequently leads people to conjecture that there is only a solution if $n\leq 2^k\leq m$. This elementary puzzle disproves that conjecture, as there are no powers of $2$ between $9$ and $13$.