Case C-257/10: Judgment of the Court (Third Chamber) of 15 December 2011 (reference for a preliminary ruling from the Högsta förvaltningsdomstolen (formerly Regeringsrätten) — Sweden) — Försäkringskassan v Elisabeth Bergström (Migrant workers — Social security — Agreement between the European Community and its Member States, of the one part, and the Swiss Confederation, of the other, on the free movement of persons — Regulation (EEC) No 1408/71 — National of a Member State who has been pursuing a professional activity in Switzerland — Return to country of origin)