Remove rows based on IF formula

[yastest]

I would like to do count of Ref based on Product. Then do if Ref is more than 1 and "Unknown" then delete the row of data.

I have thousands of row of data. Just for background I am not deleting all the Unknown rows.

Product, Description, Ref

Car    Red         1

Doll   Blue          1

Doll   Unknown  2

Thanks

[BrunPierre]

Maybe like this?

=Count(DISTINCT{$-<Ref={">1"},Description={'Unknown'}>}Ref)