For no particular reason that I can discern, Carl Nielsen is a featured composer at this year's Proms. His music entered the season rather halfheartedly last week, with performances of his cantata Springtime In Funen and a suite of his incidental music to Aladdin. But the arrival of the BBC Scottish Symphony and Osmo Vänska for the first of their three appearances at the Albert Hall this month, brought something more substantial, the Sixth Symphony, in a thoroughly convincing performance of what is a problematic score.