{HEAD ~ SELEX} is {TAIL ~ an acronym} for Systematic Evolution of Ligands by EXponential enrichment 
{ HEAD ~ SELEX } is { TAIL ~ an acronym } for Systematic Evolution of Ligands by EXponential enrichment
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH