LIN collision detection

Hi,

sorry, I don't know if I'm in the right section.

I have a question about the LIN capability detection of a collision.

I studied the specification 2.2. I understood HOW the master MANAGES a collision in case of event triggered frame. But I do not understand HOW the master KNOWS that a collision occurs. 
If we suppose that two slaves send a response, only the slave that has lost the arbitration knows it. In fact this slave sees in the bus different bits than those he injected. Perhaps this slave is able to send an error message?

Please, can you help me?

Thanks

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