In book “mastering bitcoin”, 3rd edition, page 136, there is a statement as below.
“Tx1 spends the second output of Tx0 to two new outputs, one to Alice for her share of the joint funds, and one to Bob for his share. Alice and Bob both sign this transaction before they sign Tx0.”
My question is why Alice and Bob can both sign this transaction before they sign Tx0? because tx0 id(txid 0) is the part of data to generating tx1 id.
thanks!