* <tr><th>Initial state</th><th>Tx 1</th><th>Tx 2</th><th>Result</th></tr>
* <tr><td>Empty</td><td>put(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, state is A=1</td></tr>
* <tr><td>Empty</td><td>put(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>
* <tr><th>Initial state</th><th>Tx 1</th><th>Tx 2</th><th>Result</th></tr>
* <tr><td>Empty</td><td>put(A,1)</td><td>put(A,2)</td><td>Tx 2 will fail, state is A=1</td></tr>
* <tr><td>Empty</td><td>put(A,1)</td><td>merge(A,2)</td><td>A=2</td></tr>