Filling a possible gap in the literature, we give a complete and readable proof of this trace theorem, which also shows that the imbedding constant is uniformly bounded for $T \downarrow 0$. The proof is based on a version of Hardy's inequality (cp. Appendix).
@article{116972, author = {Peter Weidemaier}, title = {The trace theorem $W^{2,1}\_p(\Omega\_T) \ni f \mapsto \nabla\_{\!x} f \in W^{1-1/p,1/2-1/2p}\_p(\partial \Omega\_T)$ revisited}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {32}, year = {1991}, pages = {307-314}, zbl = {0770.46018}, mrnumber = {1137792}, language = {en}, url = {http://dml.mathdoc.fr/item/116972} }
Weidemaier, Peter. The trace theorem $W^{2,1}_p(\Omega_T) \ni f \mapsto \nabla_{\!x} f \in W^{1-1/p,1/2-1/2p}_p(\partial \Omega_T)$ revisited. Commentationes Mathematicae Universitatis Carolinae, Tome 32 (1991) pp. 307-314. http://gdmltest.u-ga.fr/item/116972/
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