@article{MOMA_1968__72_177413,
     author = {B.-Ch. Chang and J.W. Smith},
     title = {The {Extension} {Problem} for {Functions} {Invariant} under a {Group.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {118--132},
     publisher = {mathdoc},
     volume = {72},
     year = {1968},
     zbl = {0159.53001},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1968__72_177413/}
}