Optimal limiting embeddings for $\Delta$-reduced Sobolev spaces in $L^1$
  We prove sharp embedding inequalities for certain reduced Sobolev spaces that arise naturally in the context of Dirichlet problems with $L^1$ data. We also find the optimal target spaces for such embeddings, which in dimension 2 could be considered as limiting cases of the Hansson-Brezis-Wainger spaces, for the optimal embeddings of borderline Sobolev spaces $W_0^{k,n/k}$. 
Luigi Fontana, Carlo Morpurgo
math.FA