to this:
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XXX: There are two girls.
The PD is zero.
What is?
Coefficient of productivity is zero.
I: A girl, not productive, but useful.
productive
I: is useful
Who are you studying with?
I am an engineer.
I am a philologist, I should know.
XXX: O_O
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Because of the phrase "zero" the girl is waiting for Rosenthal with villas in the philological hell.