Intersection of http://www.ncbi.nlm.nih.gov/refseq and http://www.ncbi.nlm.nih.gov/refseq
This is the CodeSystem that contains codes in both Gene Reference Sequence Collection (http://www.ncbi.nlm.nih.gov/refseq) and Gene Reference Sequence Collection (http://www.ncbi.nlm.nih.gov/refseq).