Approximation by harmonic polynomials in star-shaped domains and exponential convergence of Trefftz hp-dGFEMRalf Hiptmair, Andrea Moiola, Ilaria Perugia and Christoph SchwabESAIM: M2AN, 48 3 (2014) 727-752DOI: https://doi.org/10.1051/m2an/2013137
