[grisbi-user] Assigning a transaction to another transaction

[Gudrun]

Hi everybody,

I am going along very fine with grisbi, getting deeper with each day I use 
it. My question of today ;-)

I pay a bill and someone gives me his part of the bill some days later. So 
in Grisbi I have two transactions, a minus from my account and a plus.  No 
the bill has f.e. the category Alimentation. How can I make clear, that 
the second transaction has to be subtracted from the first one?

Thanks again for your help!
Gudrun