@article{10_4153_S000843951800005X,
     author = {Xie, Guangheng and Yang, Dachun and Yuan, Wen},
     title = {Pointwise {Characterizations} of {Even} {Order} {Sobolev} {Spaces} via {Derivatives} of {Ball} {Averages}},
     journal = {Canadian mathematical bulletin},
     pages = {681--699},
     year = {2019},
     volume = {62},
     number = {3},
     doi = {10.4153/S000843951800005X},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/S000843951800005X/}
}