(3‐Oxo‐[1, 2, 4]triazolidin‐1‐yl)bis (butane‐1‐sulfonic acid) functionalized magnetic γ‐Fe2O3 nanoparticles: A novel and heterogeneous nanocatalyst for one‐pot and efficient four‐component synthesis of novel spiro[indeno[1, 2‐b]quinoxaline derivatives. (18th March 2019)