Wang, YiYung, Po Lam2025-12-172025-12-171435-9855ORCID:/0000-0002-0441-3625/work/162951475https://hdl.handle.net/1885/733796460We prove an approximation lemma on (stratified) homogeneous groups that allows one to approximate a function in the non-isotropic Sobolev space NL 1,Q by L∞ functions, generalizing a result of Bourgain-Brezis [BB2]. We then use this to obtain a Gagliardo-Nirenberg inequality for δb on the Heisenberg group Hn.45enCompensation phenomenaCritical Sobolev embeddingDiv-curlHomogeneous groups201410.4171/JEMS/44384898023001