When there is a sequence of trades and there is no queen involved that is standing in front her rooks or her bishop, then there is no need for going through the actual sequence. You can predict the outcome by just counting the values of the pieces according to the following method.
The usual way of counting, i.e. comparing only the #attackers with the #defenders is insufficient since it doesn't take the value of the pieces into account. That gives wrong answers when one side has two rooks while the other has one or none.
The maximum gain you can get is determined by the value of the victim. You can get never more since the defender simply stops trading.
There are 2 situations.
The value of the victim exceeds the value of the first attacker.
In that case you always win wood.
The value of the victim exceeds NOT the value of the first attacker.
In that case it depends on the values and # of attackers and defenders if you will get the value of the victim or not.
- Take as many attackers as there are defenders. Take the sum total of the value of the attackers (A).
- Take as many defenders as there are attackers. Include the victim. Take the sum total of the value of the defenders (B).
- If B exceeds A, you will gain wood, otherwise you will lose wood or stay equal.
Not only for simple trades.
At first sight there is no reason to presume that this method is limited to a trade sequence that takes place on one single square. I'm going to check if it works on multiple squares too. Besides that I'm going to look especially after the role of threats.