---------------
-- Tx1
In[1]:  alex sends 0.9 coin
Out[1]: mike receives 0.8 coin

---------------
-- Tx2
In[1]:  alex sends 2.1 coin
Out[1]: mike receives 0.9 coin
Out[2]: rose receives 1.0 coin

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-- Tx2
In[1]:  alex sends 2.1 coin
In[2]:  mara sends 0.7 coin
In[3]:  mara sends 1.1 coin
In[4]:  mara sends 1.5 coin
Out[1]: mike receives 0.9 coin
Out[2]: rose receives 1.0 coin
Out[3]: mike receives 1.9 coin
Out[4]: rose receives 0.2 coin