Header compression question: duplicate header entry and current index on computing working set

Hi,

The header compression draft 3.2 says the implementation must accept
duplicate entry
in header table.
In 3.4, to compute working set from reference set of headers, the index of
entry in header table is required.
The question is, when the duplicate entries are in the header table, which
index is used as the index of working set?
My understanding of reference set of headers is that it is just a set of
name/value pairs without index. To compute working set from it, one has to
check each pair in header table and get its index in it.

Best regards,

Tatsuhiro Tsujikawa