/// Extracts an item from the set using \p pred for searching
/**
- The function is an analog of \ref cds_intrusive_EllenBinTree_rcu_extract "extract(exempt_ptr&, Q const&)"
- but \p pred is used for key compare.
+ The function is an analog of \p extract(Q const&) but \p pred is used for key compare.
\p Less has the interface like \p std::less and should meet \ref cds_intrusive_EllenBinTree_rcu_less
"predicate requirements".
\p pred must imply the same element order as the comparator used for building the tree.