Martin (1992: 230-1):
[4:164] CONJUNCTION Ben left early.Yet he felt a little tired.
CONTINUITY Ben has left;But Flo hasn't yet arrived.
The function of yet here is interpersonal: a mood Adjunct of temporality, and so it does not mark a continuity relation with the previous message.
but
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Flo
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hasn‘t
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yet
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arrived
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Subject
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Finite
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mood Adjunct: temporality
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Predicator
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Mood
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Residue
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