ATHENS, May 17 (Xinhua) -- Non-performing loans (NPLs) in Greece's banking system had been reduced by 82.8 pct in the period 2016-2021, but the outlook for the future is cloudy due to the new challenges, local officials told an online economic forum here on Tuesday. NPLs at the end of December 2021 amounted to 18.4 billion euros (19.4 billion U.S. dollars), down by 90.3 billion euros compared to March 2016, when