The GEM Benchmark: Natural Language Generation, its Evaluation and Metrics. - Sebastian Gehrmann; Tosin P. Adewumi; Karmanya Aggarwal; Pawan Sasanka Ammanamanchi; Aremu Anuoluwapo; Antoine Bosselut; Khyathi Raghavi Chandu; Miruna-Adriana Clinciu; Dipanjan Das 001; Kaustubh D. Dhole; Wanyu Du; Esin Durmus; et al. (CoRR, 2021)