The game of Ishido

The game of Ishido is played with a set of 72 runes. Each rune has a symbol and a color. There are six different symbols and colours, and each piece exists two times.

On the board of 12 x 8 squares are six runes already in their place. The randomly chosen runes must be placed next to any rune in accordance with the following rules:
If the rune has only one neighbour, it must be of the same colour and/or symbol.
If the rune has two or three neighbours, there must be at least one of the same colour and one of the same symbol. The third one could have either the same colour or the same symbol.
If the rune has four neighbours, two of them must be of the same colour and two of the same symbol. This is what is called an Ishido and it's worth a score bonus of 25 points. If you manage this more than once, the bonus will double each time.

The game ends with all runes successfully placed on the board, or when a rune cannot be placed anywhere. If the game ends with only having two or even one rune left, you get an extra bonus of 100 or rather 500. If no rune remains, this bonus will be as much as 1000 points.

The score you get is calculated as follows:
1 neighbour: 1 point
2 neighbours: 2 points
3 neighbours: 4 points
4 neighbours: 8 points
In addition to these points, you get variable bonus points for each Ishido.
Finally, you get a bonus depending how many runes remain when the game ends.