I’m reading the paper Making Snapshot Isolation Serializable，it provide an example 2.1 in Section 2.1：
SI history H1

It’a an transaction history under SI，and explains it was The H1 transactions are serializable in order: T1T2T3；as far as i known：

• If it’s serializable as T1T2T3, there should not be R3(Y1)，must be R3(Y2)
• If it’s serializable as T1T3T2, there should not be R2(X1), must be R2(X3)

Where did I go wrong in my understanding?

I have search on google and asked on poe，it didn’t worked for me.