Complex sentence: WIG, originally an acronym for Warszawski Indeks Giełdowy (Warsaw Stock Exchange Index) is the oldest index of the Warsaw Stock Exchange, introduced on the WSE first trading session on 16 April 1991.
Split into simpler sentences: WIG, originally an acronym for Warszawski Indeks Giełdowy (Warsaw Stock Exchange Index) is the oldest index for the Warsaw Stock Exchange. It was introduced on the first trading session on 16 April 1991.