PHILADELPHIA (AP) -- Bill Cosby's lawyers are arguing in a new appeals filing that it was "fundamentally unfair" to let prosecutors use Cosby's damaging deposition from a sex accuser's lawsuit against him at trial.

The filing made Tuesday largely focuses on what Cosby believes was a binding promise from a district attorney that he wouldn't be charged in the case.

A spokeswoman for the Montgomery County district attorney's office isn't commenting, but says prosecutors will file a response within a month.

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The 83-year-old Cosby is serving a three- to 10-year prison term for three counts of felony sex assault.

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