1-(chroman-2-yl)-2-((2-(6-fluorochroman-2-yl)-2-hydroxyethyl)amino)ethanol,2-[[2-(3,4-dihydro-2H-chromen-2-yl)-2-hydroxyethyl]amino]-1-(6-fluoro-3,4-dihydro-2H-chromen-2-yl)ethanol,Nebivolol impurity as antihypertensive potentiator.,Nebivolol Hydrochloride