to the entrepreneur:
This is:

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xxx: I sell car discs, set
XXX: Some people are calling.
Will you sell two of the four?
I answer them, so buy four and then sell two.
How can I sell two?
I’ll sell two of them later! ?
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Some are calling, you say?
I explained.
1st Hardly do not send, write the numbers ("I think if I have two more devices").
2nd A few is no less than two. The second number is also recorded.
Three You call the first, you confirm the possibility of sale.
4 is Sold half a set to the first, half a set to the second.

School, shit, everything has to be taught.
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The classic divorce. Once you sell the first, the second (like everyone else) no longer needs to :)