In 1919 he proved a remarkable inequality, sometimes also called Grönwall's lemma, which has attracted, and continues to attract, considerable attention in the literature (see and the references given there):
In 1919 he proved ng pansin hindi pagkakapareho, minsan tinatawag din na Grönwall's lemma, na kung saan ay attracted, at patuloy na maakit, marami pansin sa literatura (tingnan ang mga sanggunian at ang mga ibinigay na doon):