@article{MS2_1978__43_166602,
     author = {Andrzej Szulkin},
     title = {An example concerning the topological character of the zero-set of a harmonic function.},
     journal = {Mathematica Scandinavica},
     pages = {60--62},
     publisher = {mathdoc},
     volume = {43},
     year = {1978},
     zbl = {0402.31007},
     url = {http://geodesic.mathdoc.fr/item/MS2_1978__43_166602/}
}